Almost:

```js
chromeManifest: {
  dist: {
     options: {
       buildnumber: true    // is fetched from this.options()
     },
     src: 'app/scripts/background.js',
     dest: 'dist/scripts/background.js'
  }
}
```

> is there more docs of grunt?

No.

Take a look at the contrib tasks for more examples.