[meta] use npmignore to autogenerate an npmignore file

.gitignore

@@ -32,3 +32,5 @@ node_modules
 yarn.lock
 package-lock.json
 npm-shrinkwrap.json
+
+.npmignore

package.json

@@ -20,6 +20,7 @@
 	"license": "MIT",
 	"main": "index.js",
 	"scripts": {
+		"prepack": "npmignore --auto --commentLines=autogenerated",
 		"version": "auto-changelog && git add CHANGELOG.md",
 		"postversion": "auto-changelog && git add CHANGELOG.md && git commit --no-edit --amend && git tag -f \"v$(node -e \"console.log(require('./package.json').version)\")\"",
 		"prepublishOnly": "safe-publish-latest",
@@ -60,6 +61,7 @@
 		"make-arrow-function": "^1.2.0",
 		"make-async-function": "^1.0.0",
 		"make-generator-function": "^2.0.0",
+		"npmignore": "^0.3.0",
 		"nyc": "^10.3.2",
 		"object-inspect": "^1.12.2",
 		"rimraf": "^2.7.1",
@@ -95,5 +97,10 @@
 		"backfillLimit": false,
 		"hideCredit": true,
 		"startingVersion": "v1.2.5"
+	},
+	"publishConfig": {
+		"ignore": [
+			".github/workflows"
+		]
 	}
 }