DRFDocs not showing delete, post, etc. options but regular docs do?

Heyo! Thanks so much for releasing this, it is beautiful.

I am a little confused on why I'm not seeing POST/DELETE/etc. on the DRF docs version, but I can see it on the regular API docs:



Looks like I can only do GET/OPTIONS?

Here's some code:

```python
from rest_framework import viewsets, mixins

from api import serializers
from competitions.models import Competition

class CompetitionViewSet(mixins.ListModelMixin,
mixins.CreateModelMixin,
mixins.UpdateModelMixin,
mixins.DestroyModelMixin,
viewsets.GenericViewSet):
"""Tyler loves pizza!!!"""
queryset = Competition.objects.all()
serializer_class = serializers.CompetitionSerializer
```

```python
from django.conf.urls import url, include
from rest_framework import routers

from . import views

router = routers.DefaultRouter()
router.register(r'competitions', views.CompetitionViewSet)

urlpatterns = [
url(r'^', include(router.urls)),

url(r'^api-auth/', include('rest_framework.urls', namespace='rest_framework')),

url(r'^docs/', include('rest_framework_docs.urls')),
]
```

It's probably something silly I'm overlooking, thanks!

Reproduce the report with the shown CompetitionViewSet, router registration, and rest_framework_docs.urls entry point, then compare the DRF docs output with the regular API docs. Done means the documentation view exposes the POST, DELETE, and other methods provided by the viewset mixins, rather than only GET and OPTIONS.

Written by the indexing model from the issue text.