Ensure it is clear in the docs that email provider is not needed when using just Google OAuth

[Martinsos]

In docs it sounds a bit as if email provider is needed even when using just Google OAuth which is not correct, we should make sure it is clear this is not needed. Here is user feedback on this: https://discord.com/channels/686873244791210014/1236655302812762266/1236655302812762266 .