Fixed #23314 -- Tempered recommendation of storing profile data on custom user.

Thanks gavinwahl for the report.

docs/topics/auth/customizing.txt

@@ -453,6 +453,8 @@ different User model.
     :setting:`AUTH_USER_MODEL` setting in code that is executed at import
     time. ``get_user_model()`` only works once Django has imported all models.
 
+.. _specifying-custom-user-model:
+
 Specifying a custom User model
 ------------------------------
 
@@ -706,10 +708,12 @@ Extending Django's default User
 -------------------------------
 
 If you're entirely happy with Django's :class:`~django.contrib.auth.models.User`
-model and you just want to add some additional profile information, you can
+model and you just want to add some additional profile information, you could
 simply subclass ``django.contrib.auth.models.AbstractUser`` and add your
-custom profile fields. This class provides the full implementation of the
-default :class:`~django.contrib.auth.models.User` as an :ref:`abstract model
+custom profile fields, although we'd recommend a separate model as described in
+the "Model design considerations" note of :ref:`specifying-custom-user-model`.
+``AbstractUser`` provides the full implementation of the default
+:class:`~django.contrib.auth.models.User` as an :ref:`abstract model
 <abstract-base-classes>`.
 
 .. _custom-users-and-the-built-in-auth-forms: