Fixed code example.

docs/api-guide/routers.md

@@ -45,6 +45,9 @@ For example, given a method like this on the `UserViewSet` class:
     from myapp.permissions import IsAdminOrIsSelf
     from rest_framework.decorators import detail_route
     
+    class UserViewSet(ModelViewSet):
+        ...
+        
         @detail_route(methods=['post'], permission_classes=[IsAdminOrIsSelf])
         def set_password(self, request, pk=None):
             ...