Update READMEs and add keywords for npm

Author: dibenede

README.md

@@ -31,7 +31,8 @@ To use Protocol Buffers with JavaScript, you need two main components:
 Project Status
 ===
 
-This project is currently in a working state.
+As of v4.0.0, you can directly install the `protoc-gen-js` plugin from npm as
+[@protocolbuffers/protoc-gen-js](https://www.npmjs.com/package/@protocolbuffers/protoc-gen-js).
 
 **Support Status**
 

protoc_plugin/README.md

@@ -0,0 +1,25 @@
+This package is an official distribution of protoc-gen-js plugin generating
+javascript protobuf messages with protoc.
+
+Aside from this package, you will need:
+
+1. [protoc](https://github.com/protocolbuffers/protobuf/releases), the protobuf compiler.
+2. The protobuf-javascript runtime, obtainable from [npm as google-protobuf](https://www.npmjs.com/package/google-protobuf).
+
+Usage:
+
+```js
+// Assuming you installed this package as: npm install --save-dev @protocolbuffers/protoc-gen-js
+
+protoc --plugin=./node_modules/.bin/protoc-gen-js --js_out=import_style=commonjs,binary:. messages.proto <additional .proto files>
+```
+
+`protoc` will search PATH for `protoc-gen-js` if `--plugin` is omitted.
+
+This command will generate javascript protobuf files (with a `_pb.js` suffix for
+commonjs imports) alongside their respective schema files
+(e.g. `messages_pb.js`).
+
+Please see our
+[full documentation](https://github.com/protocolbuffers/protobuf-javascript/blob/main/docs/index.md)
+for more detailed usage instructions along with the generated code API.

protoc_plugin/package.json

@@ -1,9 +1,10 @@
 {
   "name": "@protocolbuffers/protoc-gen-js",
-  "version": "4.0.0",
-  "description": "Standalone distribution of the protoc-gen-js plugin for Protocol Buffers",
+  "version": "4.0.0-1",
+  "description": "Official standalone distribution of the protoc-gen-js plugin for Protocol Buffers",
   "author": "Google Protocol Buffers Team",
   "license": "BSD-3-Clause",
+  "keywords": ["protocol buffers", "protobuf", "protoc-gen-js", "google-protobuf", "protobuf-javascript"],
   "repository": {
     "type": "git",
     "url": "git+https://github.com/protocolbuffers/protobuf-javascript.git"