Explain how to add from_transport on messenger.message_handler tag

Author: ruudk

messenger.rst

@@ -1223,6 +1223,8 @@ Then, make sure to "route" your message to *both* transports:
 
 That's it! You can now consume each transport:
 
+It's also possible to specify `from_transport` as attribute on the `messenger.message_handler` tag.
+
 .. code-block:: terminal
 
     # will only call ThumbnailUploadedImageHandler when handling the message