Docs: explain what to expect from each auth method

[Martinsos]

When I was choosing which auth method to use (user&pass, email&pass, google, ...) I was having a bit of a hard time figuring out which method to use. I went for Google for example, but wasn't aware that getting it to work in production properly is quite a bit of work, because Google wants you to submit a lot of stuff in order for them to approve your Google app to a degree where anybody can signup via Google to your app (and not just limited number of whitelisted emails). They want you to upload Youtube video explaining why you need it and what not.
On the other hand, one also has to be aware that email&pass will need you to set up an email sender later.
User&pass has its own pros & cons.

What I think would be nice is if we had an introductory summary that explains what to expect from each method: what is it good for, how long / complex is it to set it up, pros and cons.

For example, Google is not easy to set up for real production, but it is very safe. Expected time to set up for development: 15 minutes. For testing in production: 20 minutes. For real production: hours.
Github might be easier, but it mostly makes sense only for developers. Expected time: 10 minutes.
And so on and on. I am making up stuff above a bit btw.