[1.5.x] Fixed #10239 - Added docs for modelform_factory

Thanks ingenieroariel for the suggestion and slurms for the review.

Backport of 71d76ec011 from master

django/forms/models.py

@@ -141,6 +141,11 @@ def fields_for_model(model, fields=None, exclude=None, widgets=None, formfield_c
     ``exclude`` is an optional list of field names. If provided, the named
     fields will be excluded from the returned fields, even if they are listed
     in the ``fields`` argument.
+
+    ``widgets`` is a dictionary of model field names mapped to a widget
+
+    ``formfield_callback`` is a callable that takes a model field and returns
+    a form field.
     """
     field_list = []
     ignored = []
@@ -371,6 +376,21 @@ class ModelForm(six.with_metaclass(ModelFormMetaclass, BaseModelForm)):
 
 def modelform_factory(model, form=ModelForm, fields=None, exclude=None,
                       formfield_callback=None,  widgets=None):
+    """
+    Returns a ModelForm containing form fields for the given model.
+
+    ``fields`` is an optional list of field names. If provided, only the named
+    fields will be included in the returned fields.
+
+    ``exclude`` is an optional list of field names. If provided, the named
+    fields will be excluded from the returned fields, even if they are listed
+    in the ``fields`` argument.
+
+    ``widgets`` is a dictionary of model field names mapped to a widget.
+
+    ``formfield_callback`` is a callable that takes a model field and returns
+    a form field.
+    """
     # Create the inner Meta class. FIXME: ideally, we should be able to
     # construct a ModelForm without creating and passing in a temporary
     # inner class.