message: docs: usage of Node.js API in README
diff: @@ -21,7 +21,7 @@ It's written in pure JavaScript, so
  $ npm install -g @teppeis/kintone-plugin-packer
  ```
  -# Usage
  +# Usage: CLI
  ```console
  $ kintone-plugin-packer [OPTIONS] PLUGIN_DIR
  @@ -51,6 +51,20 @@ and then
  $ npm run package
  ```
  +# Usage: Node.js API
  +
  +```js
  +const packer = require('@teppeis/kintone-plugin-packer');
  +const fs = require('fs');
  +
  +const buffer = createContentsZipBufferInYourSelf();
  +packer(buffer).then(output => {
  + console.log(output.id);
  + fs.writeFileSync('./private.ppk', output.privateKey);
  + fs.writeFileSync('./plugin.zip', output.plugin);
  +});
  +```
  +
  ## License
  MIT License: Teppei Sato &lt;teppeis@gmail.com&gt;
  