Add a FAQ

[agrafix]

From https://dev.yorhel.nl/doc/funcweb :

As with everything that is (supposedly) more convenient, it also comes with a slightly steeper learning curve. I haven't, for example, figured out yet how to do regular expression based routing. I don't even know if that's still possible in the latest version - the documentation isn't very clear. Likewise, it's unclear to me what the session handling does exactly (Does it store something? And where? Is there a timeout?) and how that interacts with CSRF protection. Spock seems useful, but requires more than just a cursory glance.

We should probably answer these questions in a FAQ (?) more prominently.