docs: update README

Author: Yukaii

README.md

@@ -1,5 +1,7 @@
 # HackMD API Clients
 
+This repository contains a set of packages for interacting with the [HackMD API](https://hackmd.io/).
+
 ## Node.JS
 
 See [README](./nodejs)

nodejs/README.md

@@ -1,11 +1,37 @@
 # HackMD Node.js API Client
 
+![npm](https://img.shields.io/npm/v/@hackmd/api)
+
+## About
+
+This is a Node.js client for the [HackMD API](https://hackmd.io/).
+
+You can sign up for an account at [hackmd.io](https://hackmd.io/), and then create access tokens for your projects by following the [HackMD API documentation](https://hackmd.io/@hackmd-api/developer-portal).
+
+For bugs and feature requests, please open an issue or pull request on [GitHub](https://github.com/hackmdio/api-client).
+
 ## Installation
 
 ```bash
 npm install @hackmd/api --save
 ```
 
-## Usage
+## Example
+
+```javascript
+import HackMDAPI from '@hackmd/api'
+
+const client = new HackMDAPI('YOUR_ACCESS_TOKEN' /* required */, 'https://api.hackmd.io/v1' /* optional */)
+
+client.getMe().then(me => {
+  console.log(me.email)
+})
+```
+
+## API
+
+See the [code](./src/index.ts) and [typings](./src/type.ts). The API client is written in TypeScript, so you can get auto-completion and type checking in any TypeScript Language Server powered editor or IDE.
+
+## License
 
-TODO
+MIT