Fixed #8154: Added note to docs/db-api.txt indicating that reverse() is only...

Fixed #8154: Added note to docs/db-api.txt indicating that reverse() is only useful when the QuerySet has some prior ordering


git-svn-id: http://code.djangoproject.com/svn/django/trunk@8371 bcc190cf-cafb-0310-a4f2-bffc1f526a37