example: improve nrf readme on multiple probes

examples/lakers-nrf52840/README.md

@@ -14,12 +14,12 @@ The example is configured to be ran on nRF52840-DK board.
 
 This folder's `.cargo/config.toml` configures the target (`thumbv7m-none-eabi`) and the probe-rs runner so the things should just work:
 
-    cargo run --bin initiator
-    cargo run --bin responder
+    cargo run --bin initiator -- --probe 1366:1015:000683965284
+    cargo run --bin responder -- --probe 1366:1051:001050286964
 
-You may want to prefix the commands above with e.g. PROBE_RS_PROBE=1366:1051:001050288491 in order to specify which board you want to connect to.
+Note that if there are two boards connected to your computer, we need to specify which one we want to use.
 You can get the name of your probes by running:
 
     probe-rs list
 
-You can enhance debugging by passing environment variables such as `DEFMT_LOG=trace`."
+You can enhance debugging by passing environment variables such as `DEFMT_LOG=trace`."

examples/lakers-nrf52840/src/bin/responder.rs

@@ -60,6 +60,8 @@ async fn main(spawner: Spawner) {
         mbedtls_memory_buffer_alloc_init(buffer.as_mut_ptr(), buffer.len());
     }
 
+    info!("Responder started, will wait for messages");
+
     loop {
         let mut buffer: [u8; MAX_PDU] = [0x00u8; MAX_PDU];
         let mut c_r: Option<ConnId> = None;