Fixed #7376: auth docs don't say they depend on contenttypes.

Authentication support is bundled as a Django application in

``django.contrib.auth``. To install it, do the following:

    1. Put ``'django.contrib.auth'`` in your :setting:`INSTALLED_APPS` setting.

    1. Put ``'django.contrib.auth'`` and ``'django.contrib.contenttypes'`` in

       your :setting:`INSTALLED_APPS` setting.

       (The :class:`~django.contrib.auth.models.Permisson` model in

       :mod:`django.contrib.auth` depends on :mod:`django.contrib.contenttypes`.)

    2. Run the command ``manage.py syncdb``.

Note that the default :file:`settings.py` file created by

:djadmin:`django-admin.py startproject` includes ``'django.contrib.auth'`` in

:setting:`INSTALLED_APPS` for convenience. If your :setting:`INSTALLED_APPS`

already contains ``'django.contrib.auth'``, feel free to run

:djadmin:`django-admin.py startproject` includes ``'django.contrib.auth'`` and

``'django.contrib.contenttypes'`` in :setting:`INSTALLED_APPS` for convenience.

If your :setting:`INSTALLED_APPS` already contains these apps, feel free to run

:djadmin:`manage.py syncdb` again; you can run that command as many times as

you'd like, and each time it'll only install what's needed.