Specify how to create a superuser account in dev

To do development you will need a local super user account. This is
a standard Django practice but should be documented here as well.

README.rst

@@ -69,6 +69,15 @@ Shut down and now run:
 
 Now you can run the system and see how it goes.
 
+Admin Credentials
+~~~~~~~~~~~~~~~~~
+
+To create a local administrator account run:
+
+``./manage.py createsuperuser``
+
+and enter your username, email and password. This can then be used to login to: (http://localhost:8000/admin).
+
 Base Data
 ~~~~~~~~~