[1.0.X] Added a short note to the modelforms documentation linking between

save(commit=False) and using force_insert or force_update on the Model.save()
call. Refs #8672.

Backport of r9539 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@9541 bcc190cf-cafb-0310-a4f2-bffc1f526a37