README: add a qlog to list of supported RFCs, add an example

README.md

@@ -12,6 +12,7 @@ In addition to these base RFCs, it also implements the following RFCs:
 * Unreliable Datagram Extension ([RFC 9221](https://datatracker.ietf.org/doc/html/rfc9221))
 * Datagram Packetization Layer Path MTU Discovery (DPLPMTUD, [RFC 8899](https://datatracker.ietf.org/doc/html/rfc8899))
 * QUIC Version 2 ([RFC 9369](https://datatracker.ietf.org/doc/html/rfc9369))
+* QUIC Event Logging using qlog ([draft-ietf-quic-qlog-main-schema](https://datatracker.ietf.org/doc/draft-ietf-quic-qlog-main-schema/) and [draft-ietf-quic-qlog-quic-events](https://datatracker.ietf.org/doc/draft-ietf-quic-qlog-quic-events/))
 
 ## Using QUIC
 
@@ -174,6 +175,30 @@ msg, err := conn.ReceiveMessage()
 
 Note that this code path is currently not optimized. It works for datagrams that are sent occasionally, but it doesn't achieve the same throughput as writing data on a stream. Please get in touch on issue #3766 if your use case relies on high datagram throughput, or if you'd like to help fix this issue. There are also some restrictions regarding the maximum message size (see #3599).
 
+### QUIC Event Logging using qlog
+
+quic-go logs a wide range of events defined in [draft-ietf-quic-qlog-quic-events](https://datatracker.ietf.org/doc/draft-ietf-quic-qlog-quic-events/), providing comprehensive insights in the internals of a QUIC connection. 
+
+qlog files can be processed by a number of 3rd-party tools. [qviz](https://qvis.quictools.info/) has proven very useful for debugging all kinds of QUIC connection failures.
+
+qlog is activated by setting a `Tracer` callback on the `Config`. It is called as soon as quic-go decides to starts the QUIC handshake on a new connection.
+A useful implementation of this callback could look like this:
+```go
+quic.Config{
+  Tracer: func(ctx context.Context, p logging.Perspective, connID quic.ConnectionID) *logging.ConnectionTracer {
+    role := "server"
+    if p == logging.PerspectiveClient {
+      role = "client"
+    }
+    filename := fmt.Sprintf("./log_%x_%s.qlog", connID, role)
+    f, err := os.Create(filename)
+    // handle the error
+    return qlog.NewConnectionTracer(f, p, connID)
+  }
+}
+```
+
+This implementation of the callback creates a new qlog file in the current directory named `log_<client / server>_<QUIC connection ID>.qlog`.
 
 
 ## Using HTTP/3