Fixed #20294 -- Documented context processors in TemplateResponseMixin.

        altered later (e.g. in

        :ref:`template response middleware <template-response-middleware>`).

        .. admonition:: Context processors

            ``TemplateResponse`` uses :class:`~django.template.RequestContext`

            which  means that callables defined in

            :setting:`TEMPLATE_CONTEXT_PROCESSORS` may overwrite template

            variables defined in your views. For example, if you subclass

            :class:`DetailView <django.views.generic.detail.DetailView>` and

            set ``context_object_name`` to ``user``, the

            ``django.contrib.auth.context_processors.auth`` context processor

            will happily overwrite your variable with current user.

        If you need custom template loading or custom context object

        instantiation, create a ``TemplateResponse`` subclass and assign it to

        ``response_class``.