Update throttling.md (#7606)

There were recent updates to the `@action` decorator calling a little more attention to the kwargs it accepts. 
I thought it would be useful to also provide an example in the throttling section of how those kwargs can be used to define/override throttle_classes through the action decorator as well.

Author: 144mdgross

docs/api-guide/throttling.md

@@ -59,7 +59,7 @@ using the `APIView` class-based views.
             }
             return Response(content)
 
-Or, if you're using the `@api_view` decorator with function based views.
+If you're using the `@api_view` decorator with function based views you can use the following decorator.
 
     @api_view(['GET'])
     @throttle_classes([UserRateThrottle])
@@ -69,6 +69,16 @@ Or, if you're using the `@api_view` decorator with function based views.
         }
         return Response(content)
 
+It's also possible to set throttle classes for routes that are created using the `@action` decorator.
+Throttle classes set in this way will override any viewset level class settings.
+
+    @action(detail=True, methods=["post"], throttle_classes=[UserRateThrottle])
+    def example_adhoc_method(request, pk=None):
+        content = {
+            'status': 'request was permitted'
+        }
+        return Response(content)
+
 ## How clients are identified
 
 The `X-Forwarded-For` HTTP header and `REMOTE_ADDR` WSGI variable are used to uniquely identify client IP addresses for throttling.  If the `X-Forwarded-For` header is present then it will be used, otherwise the value of the `REMOTE_ADDR` variable from the WSGI environment will be used.