Fixed #21712 -- Moved autodiscover() to AdminConfig.ready().

Thanks Marc Tamlyn for the initial version of the patch.

docs/intro/tutorial01.txt

@@ -435,7 +435,7 @@ look like this:
     :filename: mysite/settings.py
 
     INSTALLED_APPS = (
-        'django.contrib.admin',
+        'django.contrib.admin.apps.AdminConfig',
         'django.contrib.auth',
         'django.contrib.contenttypes',
         'django.contrib.sessions',
@@ -444,6 +444,13 @@ look like this:
         'polls',
     )
 
+.. admonition:: Doesn't match what you see?
+
+    If you're seeing ``'django.contrib.admin'`` instead of
+    ``'django.contrib.admin.apps.AdminConfig'``, you're probably using a
+    version of Django that doesn't match this tutorial version.  You'll want
+    to either switch to the older tutorial or the newer Django version.
+
 Now Django knows to include the ``polls`` app. Let's run another command:
 
 .. code-block:: bash