fix: add example metrics's tracing::info

Adding a Minimal `println!()` Syntax for Metrics Example

Pull-Request: libp2p#5440.

Author: elecbug

examples/metrics/src/main.rs

@@ -66,6 +66,13 @@ async fn main() -> Result<(), Box<dyn Error>> {
 
     loop {
         match swarm.select_next_some().await {
+            SwarmEvent::NewListenAddr { address, .. } => {
+                tracing::info!(
+                    "Local node is listening on\n {}/p2p/{}",
+                    address,
+                    swarm.local_peer_id()
+                );
+            }
             SwarmEvent::Behaviour(BehaviourEvent::Ping(ping_event)) => {
                 tracing::info!(?ping_event);
                 metrics.record(&ping_event);