Fix redirect URI.
Fix redirect URI.

This special URI tells Google to display a code with along instructions to
copy-paste it.

Added some instructional comments to help configure the Google API project
properly. Also simplified the prompt for code (parameter).

maxcountryman/rauth,maxcountryman/rauth,isouzasoares/rauth,arifgursel/rauth,arifgursel/rauth,arifgursel/rauth,isouzasoares/rauth,litl/rauth,litl/rauth