[1.1.X] Fixed #11883: Documented how to set a custom template name on a...

[1.1.X] Fixed #11883: Documented how to set a custom template name on a flatpage. Backport of [12667] from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@12668 bcc190cf-cafb-0310-a4f2-bffc1f526a37