Docs: There is no overview for FoF flags or how to use them

[Holmus]

When trying to set up Google OAuth via FoF, I noticed that:

1. The Google OAuth flag is never clearly referenced where it is mentioned (there is a link loop here and here
2. There is no clear table or overview at all to reference all FoF flags that can be set.

Not sure whether we should do 2 but we should fix 1