Add note about two methods which must not be called from main thread.

Signed-off-by: Aron Cedercrantz <aron@cedercrantz.se>
Merge branch 'master' of https://github.com/opfo/app

* 'master' of https://github.com/opfo/app:
  Commented out the PostQuestion view in master while I'm fixing a bug
  Added view and controllers for posting questions. Functionality is not fully implemented yet.