Update READMEs for yarn (babel#8215) [skip ci]

Closes babel#8255

packages/babel-cli/README.md

@@ -9,11 +9,11 @@ See our website [@babel/cli](https://babeljs.io/docs/en/next/babel-cli.html) for
 Using npm:
 
 ```sh
-npm install --save @babel/cli
+npm install --save-dev @babel/cli
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/cli
+yarn add @babel/cli --dev
 ```

packages/babel-code-frame/README.md

@@ -9,11 +9,11 @@ See our website [@babel/code-frame](https://babeljs.io/docs/en/next/babel-code-f
 Using npm:
 
 ```sh
-npm install --save @babel/code-frame
+npm install --save-dev @babel/code-frame
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/code-frame
+yarn add @babel/code-frame --dev
 ```

packages/babel-core/README.md

@@ -9,11 +9,11 @@ See our website [@babel/core](https://babeljs.io/docs/en/next/babel-core.html) f
 Using npm:
 
 ```sh
-npm install --save @babel/core
+npm install --save-dev @babel/core
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/core
+yarn add @babel/core --dev
 ```

packages/babel-generator/README.md

@@ -9,11 +9,11 @@ See our website [@babel/generator](https://babeljs.io/docs/en/next/babel-generat
 Using npm:
 
 ```sh
-npm install --save @babel/generator
+npm install --save-dev @babel/generator
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/generator
+yarn add @babel/generator --dev
 ```

packages/babel-helper-annotate-as-pure/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-annotate-as-pure](https://babeljs.io/docs/en/next
 Using npm:
 
 ```sh
-npm install --save @babel/helper-annotate-as-pure
+npm install --save-dev @babel/helper-annotate-as-pure
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-annotate-as-pure
+yarn add @babel/helper-annotate-as-pure --dev
 ```

packages/babel-helper-bindify-decorators/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-bindify-decorators](https://babeljs.io/docs/en/ne
 Using npm:
 
 ```sh
-npm install --save @babel/helper-bindify-decorators
+npm install --save-dev @babel/helper-bindify-decorators
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-bindify-decorators
+yarn add @babel/helper-bindify-decorators --dev
 ```

packages/babel-helper-builder-binary-assignment-operator-visitor/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-builder-binary-assignment-operator-visitor](https
 Using npm:
 
 ```sh
-npm install --save @babel/helper-builder-binary-assignment-operator-visitor
+npm install --save-dev @babel/helper-builder-binary-assignment-operator-visitor
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-builder-binary-assignment-operator-visitor
+yarn add @babel/helper-builder-binary-assignment-operator-visitor --dev
 ```

packages/babel-helper-builder-react-jsx/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-builder-react-jsx](https://babeljs.io/docs/en/nex
 Using npm:
 
 ```sh
-npm install --save @babel/helper-builder-react-jsx
+npm install --save-dev @babel/helper-builder-react-jsx
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-builder-react-jsx
+yarn add @babel/helper-builder-react-jsx --dev
 ```

packages/babel-helper-call-delegate/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-call-delegate](https://babeljs.io/docs/en/next/ba
 Using npm:
 
 ```sh
-npm install --save @babel/helper-call-delegate
+npm install --save-dev @babel/helper-call-delegate
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-call-delegate
+yarn add @babel/helper-call-delegate --dev
 ```

packages/babel-helper-define-map/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-define-map](https://babeljs.io/docs/en/next/babel
 Using npm:
 
 ```sh
-npm install --save @babel/helper-define-map
+npm install --save-dev @babel/helper-define-map
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-define-map
+yarn add @babel/helper-define-map --dev
 ```

packages/babel-helper-explode-assignable-expression/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-explode-assignable-expression](https://babeljs.io
 Using npm:
 
 ```sh
-npm install --save @babel/helper-explode-assignable-expression
+npm install --save-dev @babel/helper-explode-assignable-expression
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-explode-assignable-expression
+yarn add @babel/helper-explode-assignable-expression --dev
 ```

packages/babel-helper-explode-class/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-explode-class](https://babeljs.io/docs/en/next/ba
 Using npm:
 
 ```sh
-npm install --save @babel/helper-explode-class
+npm install --save-dev @babel/helper-explode-class
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-explode-class
+yarn add @babel/helper-explode-class --dev
 ```

packages/babel-helper-fixtures/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-fixtures](https://babeljs.io/docs/en/next/babel-h
 Using npm:
 
 ```sh
-npm install --save @babel/helper-fixtures
+npm install --save-dev @babel/helper-fixtures
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-fixtures
+yarn add @babel/helper-fixtures --dev
 ```

packages/babel-helper-function-name/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-function-name](https://babeljs.io/docs/en/next/ba
 Using npm:
 
 ```sh
-npm install --save @babel/helper-function-name
+npm install --save-dev @babel/helper-function-name
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-function-name
+yarn add @babel/helper-function-name --dev
 ```

packages/babel-helper-get-function-arity/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-get-function-arity](https://babeljs.io/docs/en/ne
 Using npm:
 
 ```sh
-npm install --save @babel/helper-get-function-arity
+npm install --save-dev @babel/helper-get-function-arity
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-get-function-arity
+yarn add @babel/helper-get-function-arity --dev
 ```

packages/babel-helper-hoist-variables/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-hoist-variables](https://babeljs.io/docs/en/next/
 Using npm:
 
 ```sh
-npm install --save @babel/helper-hoist-variables
+npm install --save-dev @babel/helper-hoist-variables
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-hoist-variables
+yarn add @babel/helper-hoist-variables --dev
 ```

packages/babel-helper-member-expression-to-functions/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-member-expression-to-functions](https://babeljs.i
 Using npm:
 
 ```sh
-npm install --save @babel/helper-member-expression-to-functions
+npm install --save-dev @babel/helper-member-expression-to-functions
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-member-expression-to-functions
+yarn add @babel/helper-member-expression-to-functions --dev
 ```

packages/babel-helper-module-imports/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-module-imports](https://babeljs.io/docs/en/next/b
 Using npm:
 
 ```sh
-npm install --save @babel/helper-module-imports
+npm install --save-dev @babel/helper-module-imports
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-module-imports
+yarn add @babel/helper-module-imports --dev
 ```

packages/babel-helper-module-transforms/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-module-transforms](https://babeljs.io/docs/en/nex
 Using npm:
 
 ```sh
-npm install --save @babel/helper-module-transforms
+npm install --save-dev @babel/helper-module-transforms
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-module-transforms
+yarn add @babel/helper-module-transforms --dev
 ```

packages/babel-helper-optimise-call-expression/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-optimise-call-expression](https://babeljs.io/docs
 Using npm:
 
 ```sh
-npm install --save @babel/helper-optimise-call-expression
+npm install --save-dev @babel/helper-optimise-call-expression
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-optimise-call-expression
+yarn add @babel/helper-optimise-call-expression --dev
 ```

packages/babel-helper-plugin-test-runner/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-plugin-test-runner](https://babeljs.io/docs/en/ne
 Using npm:
 
 ```sh
-npm install --save @babel/helper-plugin-test-runner
+npm install --save-dev @babel/helper-plugin-test-runner
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-plugin-test-runner
+yarn add @babel/helper-plugin-test-runner --dev
 ```

packages/babel-helper-plugin-utils/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-plugin-utils](https://babeljs.io/docs/en/next/bab
 Using npm:
 
 ```sh
-npm install --save @babel/helper-plugin-utils
+npm install --save-dev @babel/helper-plugin-utils
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-plugin-utils
+yarn add @babel/helper-plugin-utils --dev
 ```

packages/babel-helper-regex/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-regex](https://babeljs.io/docs/en/next/babel-help
 Using npm:
 
 ```sh
-npm install --save @babel/helper-regex
+npm install --save-dev @babel/helper-regex
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-regex
+yarn add @babel/helper-regex --dev
 ```

packages/babel-helper-remap-async-to-generator/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-remap-async-to-generator](https://babeljs.io/docs
 Using npm:
 
 ```sh
-npm install --save @babel/helper-remap-async-to-generator
+npm install --save-dev @babel/helper-remap-async-to-generator
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-remap-async-to-generator
+yarn add @babel/helper-remap-async-to-generator --dev
 ```

packages/babel-helper-replace-supers/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-replace-supers](https://babeljs.io/docs/en/next/b
 Using npm:
 
 ```sh
-npm install --save @babel/helper-replace-supers
+npm install --save-dev @babel/helper-replace-supers
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-replace-supers
+yarn add @babel/helper-replace-supers --dev
 ```

packages/babel-helper-simple-access/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-simple-access](https://babeljs.io/docs/en/next/ba
 Using npm:
 
 ```sh
-npm install --save @babel/helper-simple-access
+npm install --save-dev @babel/helper-simple-access
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-simple-access
+yarn add @babel/helper-simple-access --dev
 ```

packages/babel-helper-split-export-declaration/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-split-export-declaration](https://babeljs.io/docs
 Using npm:
 
 ```sh
-npm install --save @babel/helper-split-export-declaration
+npm install --save-dev @babel/helper-split-export-declaration
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-split-export-declaration
+yarn add @babel/helper-split-export-declaration --dev
 ```

packages/babel-helper-transform-fixture-test-runner/README.md

@@ -9,11 +9,11 @@ See our website [@babel/helper-transform-fixture-test-runner](https://babeljs.io
 Using npm:
 
 ```sh
-npm install --save @babel/helper-transform-fixture-test-runner
+npm install --save-dev @babel/helper-transform-fixture-test-runner
 ```
 
 or using yarn:
 
 ```sh
-yarn add --save @babel/helper-transform-fixture-test-runner
+yarn add @babel/helper-transform-fixture-test-runner --dev
 ```