Fixed #23067 Update docs to use django-admin instead of django-admin.py

Updated the documentation to use django-admin term instead of the old
django-admin.py

Patch for ticket #23067: https://code.djangoproject.com/ticket/23067
we should add a `.. versionchanged:: 1.7` note below this to let readers know that if this doesn't work, they are likely using the wrong version of the tutorial for the version of Django they have installed.