docs(sources/companion-plugins/google-drive): adds information on required app scopes.

[matthewhartstonge]

Took me a little code diving/GH issue spelunking to find this, so thought it might be nice to add it to the docs for others/my future self 👍

Refer:

• https://github.com/transloadit/uppy/blob/37d0a03390b4e704949dbe5f2bfc9e116e3cba1c/packages/%40uppy/companion/src/config/grant.js#L8
• https://github.com/transloadit/uppy/issues/2288
• https://github.com/transloadit/uppy/issues/4793