[1.0.X] Added a note about where custom manager specifications go in a model

(for the style guide).

Backport of r9191 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@9194 bcc190cf-cafb-0310-a4f2-bffc1f526a37

docs/internals/contributing.txt

@@ -555,6 +555,7 @@ Model style
       follows (noting that these are not all required):
 
         * All database fields
+        * Custom manager attributes
         * ``class Meta``
         * ``def __unicode__()``
         * ``def __str__()``