Fixed #17638 -- Added crosslinks between topic and reference guides.

Thanks oinopion for the suggestion and jarus for the initial patch.

docs/topics/db/models.txt

@@ -1374,3 +1374,9 @@ different database tables).
 
 Django will raise a :exc:`~django.core.exceptions.FieldError` if you override
 any model field in any ancestor model.
+
+.. seealso::
+
+    :doc:`The Models Reference </ref/models/index>`
+        Covers all the model related APIs including model fields, related
+        objects, and ``QuerySet``.

docs/topics/migrations.txt

@@ -667,3 +667,9 @@ your Django migrations in the ``migrations`` directory.
 
 More information is available in the
 `South 1.0 release notes <http://south.readthedocs.org/en/latest/releasenotes/1.0.html#library-migration-path>`_.
+
+.. seealso::
+
+    :doc:`The Migrations Operations Reference </ref/migration-operations>`
+        Covers the schema operations API, special operations, and writing your
+        own operations.

docs/topics/settings.txt

@@ -267,3 +267,8 @@ It boils down to this: Use exactly one of either ``configure()`` or
 ``DJANGO_SETTINGS_MODULE``. Not both, and not neither.
 
 .. _@login_required: ../authentication/#the-login-required-decorator
+
+.. seealso::
+
+    :doc:`The Settings Reference </ref/settings>`
+        Contains the complete list of core and contrib app settings.

docs/topics/templates.txt

@@ -693,3 +693,9 @@ access to the humanize template tags and filters. The child template is
 responsible for its own ``{% load humanize %}``.
 
 This is a feature for the sake of maintainability and sanity.
+
+.. seealso::
+
+    :doc:`The Templates Reference </ref/templates/index>`
+        Covers built-in tags, built-in filters, using an alternative template,
+        language, and more.