Document documentation.py (#5478)
Document documentation.py (#5478)

Closes #5198. Closes #5142. Closes #4980
kgeorgy/django-rest-framework,dmwyatt/django-rest-framework,tomchristie/django-rest-framework,tomchristie/django-rest-framework,jpadilla/django-rest-framework,kgeorgy/django-rest-framework,tomchristie/django-rest-framework,dmwyatt/django-rest-framework,jpadilla/django-rest-framework,dmwyatt/django-rest-framework,kgeorgy/django-rest-framework,jpadilla/django-rest-framework