Document that the bytes_received signal is not yet implemented for HTTP/2

docs/topics/settings.rst

@@ -703,6 +703,8 @@ The default HTTPS handler uses HTTP/1.1. To use HTTP/2 update
 
     -   No support for `server pushes`_, which are ignored.
 
+    -   No support for the :signal:`bytes_received` signal.
+
 .. _frame size: https://tools.ietf.org/html/rfc7540#section-4.2
 .. _http2 faq: https://http2.github.io/faq/#does-http2-require-encryption
 .. _server pushes: https://tools.ietf.org/html/rfc7540#section-8.2