Add elevator pitch to README

README.rst

@@ -7,7 +7,17 @@ django-sudo
 .. image:: https://coveralls.io/repos/mattrobenolt/django-sudo/badge.png?branch=master
    :target: https://coveralls.io/r/mattrobenolt/django-sudo?branch=master
 
-Sudo mode is an extra layer of security for your most sensitive pages.
+``django-sudo`` is an implementation of GitHub's `Sudo Mode
+<https://github.com/blog/1513-introducing-github-sudo-mode>`_ for `Django
+<https://www.djangoproject.com/>`_.
+
+What is this for?
+~~~~~~~~~~~~~~~~~
+``django-sudo`` provides an extra layer of security for after a user is already logged in. Views can
+be decorated with :func:`@sudo_required <django_sudo.decorators.sudo_required>`, and then a user
+must re-enter their password to view that page. After verifying their password, that user has
+elevated permissions for the duration of ``SUDO_COOKIE_AGE``. This duration is independent of the
+normal session duration allowing short elevated permission durations, but retain long user sessions.
 
 Installation
 ~~~~~~~~~~~~