* installation for django added in requirements.txt
* added line to install django first in contributing.md
* added line to install django first in contributing.md and CONTRIBUTING.md
As per [their blog post of the 27th April](https://blog.readthedocs.com/securing-subdomains/) ‘Securing subdomains’:
> Starting today, Read the Docs will start hosting projects from subdomains on the domain readthedocs.io, instead of on readthedocs.org. This change addresses some security concerns around site cookies while hosting user generated data on the same domain as our dashboard.
Test Plan: Manually visited all the links I’ve modified.
* Get rid of runtests.py
* Moved test code from rest_framework/tests and rest_framework/runtests to tests
* Invoke py.test from setup.py
* Invoke py.test from Travis
* Invoke py.test from tox
* Changed setUpClass to be just plain setUp in test_permissions.py
* Updated contribution guideline to show how to invoke py.test