Explain that "authenticated user" role is required by other user roles

Any logged-in Drupal user is always assigned to the "authenticated user" role in addition to any other roles. Therefore, on the Authcache Configuration screen you must select "authenticated user (without additional roles)" if you select any other roles. If you select other roles but leave "authenticated user" unselected, then a user belonging to one of the selected roles will not get cached content.

This requirement could be made clearer (or even forced) on the Authcache Configuration screen.