Fixed #20609 -- Documented how to use request.user with RequestFactory

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

    import unittest

    from django.contrib.auth.models import User

    from django.test import TestCase

    from django.test.client import RequestFactory

    class SimpleTest(unittest.TestCase):

    class SimpleTest(TestCase):

        def setUp(self):

            # Every test needs access to the request factory.

            self.factory = RequestFactory()

            self.user = User.objects.create_user(

                first_name='jacob', email='jacob@…', password='top_secret')

        def test_details(self):

            # Create an instance of a GET request.

            request = self.factory.get('/customer/details')

            # Recall that middleware are not suported. You can simulate a

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

            request.user = self.user

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

            response = my_view(request)

            self.assertEqual(response.status_code, 200)