[1.0.X] Fixed #10367: Added note to generic-relation docs explaining when it's...

[1.0.X] Fixed #10367: Added note to generic-relation docs explaining when it's necessary to pass in field names to create a reverse relation. Backport of [10273] from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@10274 bcc190cf-cafb-0310-a4f2-bffc1f526a37