Include a comparison to django-redis in the readme

[edmorley]

An alternative Django redis package is django-redis: https://github.com/niwinz/django-redis http://niwinz.github.io/django-redis/latest/

To assist with people trying to decide between them, it would be good to have a quick comparison either in the readme or the read the docs intro section :-)

(My searches only found http://stackoverflow.com/questions/21932097/difference-between-django-redis-cache-and-django-redis-for-redis-caching-with-dj)