Fixed #6120: First stab at documenting newforms field types which handle relationships.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@7298 bcc190cf-cafb-0310-a4f2-bffc1f526a37

docs/newforms.txt

@@ -1499,6 +1499,33 @@ the bottom of this document, for examples of their use.
 ``SplitDateTimeField``
 ~~~~~~~~~~~~~~~~~~~~~~
 
+Fields which handle relationships
+---------------------------------
+
+For representing relationships between models, two fields are
+provided which can derive their choices from a ``QuerySet``, and which
+place one or more model objects into the ``cleaned_data`` dictionary
+of forms in which they're used. Both of these fields have an
+additional required argument:
+
+``queryset``
+    A ``QuerySet`` of model objects from which the choices for the
+    field will be derived, and which will be used to validate the
+    user's selection.
+
+``ModelChoiceField``
+~~~~~~~~~~~~~~~~~~~~
+
+Allows the selection of a single model object, suitable for
+representing a foreign key.
+
+``ModelMultipleChoiceField``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Allows the selection of one or more model objects, suitable for
+representing a many-to-many relation.
+
+
 Creating custom fields
 ----------------------