rust: enhance README.md

Signed-off-by: Nicolas Buffon <nicolas.buffon@orange.com>

Author: nbuffon

rust/README.md

@@ -1,21 +1,22 @@
-libits
-======
+libits-client
+=============
 
 [![Build Status](https://github.com/Orange-OpenSource/its-client/workflows/Rust/badge.svg)][1]
 [![crates.io](https://img.shields.io/crates/v/its-client)][2]
 
-The Intelligent Transportation Systems (ITS) [MQTT][3] Rust package based on
-the [JSON][4] [ETSI][5] specification transcription.
+MQTv5
+TELEMETRY
+
 
 Examples
 --------
 
-By default, all example logs into `./log/<example>_rCURRENT.log`
-You can inspect the logs using `tail -F log/its-client_rCURRENT.log`
-
 ### json_counter
 
-Subscribes to `test.mosquitto.org` and yields how much messages were received and the number of them that had JSON payload
+Demonstrates how to use the IoT3 message exchange feature.
+
+Subscribes to `test.mosquitto.org` and yields how much messages were received
+and the number of them whose payload is in JSON.
 
 ```
 cargo run --example json_counter
@@ -26,10 +27,30 @@ Logs are redirected to a file
 tail -F log/json_counter_rCURRENT.log
 ```
 
+### telemetry
+
+This example describes how to send OpenTelemetry traces and how to transmit W3C context to link spans between traces. 
+
+We don't expose any public OTLP collector (yet?), so you either have to:
+- use one of your own already available
+or
+- spawn one
+  ```
+  docker run ... TODO
+  ```
+In any case, before running the example, you must edit the `[telemetry]` section of configuration
+with the proper values.  
+Then you can run the example:
+```
+cargo run --example telemetry --features telemetry
+```
+
 ### copycat
 
 Subscribes to ITS CAM and CPM messages, stores them and sends a copy 3 seconds later
 
+TODO telemetry link propagation through user properties
+
 [1]: https://github.com/Orange-OpenSource/its-client/actions/workflows/rust.yml
 [2]: https://crates.io/crates/its-client
 [3]: https://mqtt.org/