Fixed #20609 -- Added instructions for using AnonymousUser with RequestFactory.

The following is a simple unit test using the request factory::

    from django.contrib.auth.models import User

    from django.contrib.auth.models import AnonymousUser, User

    from django.test import TestCase, RequestFactory

    class SimpleTest(TestCase):

            # logged-in user by setting request.user manually.

            request.user = self.user

            # Or you can simulate an anonymous user by setting request.user to

            # an AnonymousUser instance.

            request.user = AnonymousUser()

            # Test my_view() as if it were deployed at /customer/details

            response = my_view(request)

            self.assertEqual(response.status_code, 200)