Document further changes necessary when upgrading Django

The main issue is that Oscar relies on it's app configs to keep class
loading working. Hence, appropriate app configs need to be created when
upgrading.

docs/source/releases/v0.8.rst

 migrations framework.
 Unfortunately, the changes in Django required a few breaking changes when
 upgrading Oscar both for users staying on Django 1.6 and for users upgrading to
-Django 1.7 at the same time.
+Django 1.7 at the same time. These are detailed in the section for
+backwards-incompatible changes.
 
 Reworked shipping app
 ~~~~~~~~~~~~~~~~~~~~~
    ``oscar_find_duplicate_emails`` management command to check your database
    and deal with any conflicts accordingly.
 
+Django 1.7 support
+------------------
+
+If you have any plans to upgrade to Django 1.7, more changes beyond
+addressing migrations are necessary:
+
+* You should be aware that Django 1.7 now enforces uniqueness of app labels.
+  Oscar dashboard apps now ship with app configs that set their app label
+  to ``{oldname}_dashboard``.
+* If you have forked any Oscar apps, you must add app configs to them, and
+  have them inherit from the Oscar one. See the appropriate section in
+  :doc:`/topics/fork_app` for an example.
+* Double-check that you address migrations as detailed above.
+* Django now enforces that no calls happen to the model registry during
+  app startup. This mostly means that you should avoid module-level calls to
+  ``get_model``, as that only works with a fully initialised model registry.
+
 Misc
 ~~~~