[3.1.x] Refs #9475 -- Linked through_default docs to related managers…

… methods.

Backport of 284bde3 from master

docs/topics/db/models.txt

@@ -521,8 +521,11 @@ the intermediate model::
     >>> beatles.members.all()
     <QuerySet [<Person: Ringo Starr>, <Person: Paul McCartney>]>
 
-You can also use ``add()``, ``create()``, or ``set()`` to create relationships,
-as long as you specify ``through_defaults`` for any required fields::
+You can also use :meth:`~django.db.models.fields.related.RelatedManager.add`,
+:meth:`~django.db.models.fields.related.RelatedManager.create`, or
+:meth:`~django.db.models.fields.related.RelatedManager.set` to create
+relationships, as long as you specify ``through_defaults`` for any required
+fields::
 
     >>> beatles.members.add(john, through_defaults={'date_joined': date(1960, 8, 1)})
     >>> beatles.members.create(name="George Harrison", through_defaults={'date_joined': date(1960, 8, 1)})