Updated README with notes on mod_wsgi backend
Updated README with notes on mod_wsgi backend

In particular how to use mod_rewrite to make /private/ only accessible
via an internal redirect.

johnsensible/django-sendfile,NotSqrt/django-sendfile,joshcartme/django-sendfile,karyon/django-sendfile,joshcartme/django-sendfile,nathanielvarona/django-sendfile