Issue #1707: Add documentation to api-docs.viewsets notifying users
that they should use the get_queryset() method when overriding a
ModelViewSet method, such as list(). Otherwise, since queryset is
a static property, the value will be cached for every instance of
that ViewSet.
Issue #1707 - Add documentation about the caching of `GenericAPIView.queryset`
to the `queryset` property, `get_queryset()`, and do generic-views.md; remove
changes to the viewsets.md documentation from my last commit.
Issue #1707 - Add info about queryset property caching to get_queryset() docs.

Add documentation to the get_queryset() method of generic-views.md regarding
the caching of the queryset property.
Merge pull request #1711 from kdazzle/ModelViewSet-queryset-static-property

Issue #1707: Add documentation to api-docs.viewsets