Corrected docs on router include with namespaces. (encode#5843)

* Provide both app and instance namespace examples
* Emphasise non-namespaced option

Author: carltongibson

docs/api-guide/routers.md

@@ -72,14 +72,32 @@ Alternatively you can use Django's `include` function, like so…
         url(r'^', include(router.urls)),
     ]
 
-Router URL patterns can also be namespaces.
+You may use `include` with an application namespace:
 
     urlpatterns = [
         url(r'^forgot-password/$', ForgotPasswordFormView.as_view()),
-        url(r'^api/', include(router.urls, namespace='api')),
+        url(r'^api/', include((router.urls, 'app_name'))),
     ]
 
-If using namespacing with hyperlinked serializers you'll also need to ensure that any `view_name` parameters on the serializers correctly reflect the namespace. In the example above you'd need to include a parameter such as `view_name='api:user-detail'` for serializer fields hyperlinked to the user detail view.
+Or both an application and instance namespace:
+
+    urlpatterns = [
+        url(r'^forgot-password/$', ForgotPasswordFormView.as_view()),
+        url(r'^api/', include((router.urls, 'app_name'), namespace='instance_name')),
+    ]
+
+See Django's [URL namespaces docs][url-namespace-docs] and the [`include` API reference][include-api-reference] for more details.
+
+---
+
+**Note**: If using namespacing with hyperlinked serializers you'll also need to ensure that any `view_name` parameters
+on the serializers correctly reflect the namespace. In the examples above you'd need to include a parameter such as
+`view_name='app_name:user-detail'` for serializer fields hyperlinked to the user detail view.
+
+The automatic `view_name` generation uses a pattern like `%(model_name)-detail`. Unless your models names actually clash
+you may be better off **not** namespacing your Django REST Framework views when using hyperlinked serializers.
+
+---
 
 ### Routing for extra actions
 
@@ -315,3 +333,5 @@ The [`DRF-extensions` package][drf-extensions] provides [routers][drf-extensions
 [drf-extensions-nested-viewsets]: https://chibisov.github.io/drf-extensions/docs/#nested-routes
 [drf-extensions-collection-level-controllers]: https://chibisov.github.io/drf-extensions/docs/#collection-level-controllers
 [drf-extensions-customizable-endpoint-names]: https://chibisov.github.io/drf-extensions/docs/#controller-endpoint-name
+[url-namespace-docs]: https://docs.djangoproject.com/en/1.11/topics/http/urls/#url-namespaces
+[include-api-reference]: https://docs.djangoproject.com/en/2.0/ref/urls/#include