Improve documentation of Google-apis oauth flow

I went through learning to work with the Oauth flow, and it definitely is a bit convoluted. Maybe include a note to refer to GAPI docs and include a simple oauth flow example? such as:

```
  API = event.target
  API.auth.authorize({
    client_id: 'CLIENT ID',
    immediate: true,
    scope: 'SPACE DELIMITED SCOPES'
  },function(e){console.log(e)})
```
