Use the target actually mentioned in the .cargo/config file.
Updated the output in the troubleshooting page and
also updated the target for the board/dongle.
and adjust puzzle-radio starter code accordingly
this reduces the chance of people using puzzle-radio with the wrong dongle
app (i.e. loopback); that would lead to them getting response different than
what's indicated in the text
I have also added the app name to the dongle / serial-term output:
``` text
deviceid=75fa82ad7588b3c7 channel=20 TxPower=+8dBm app=loopback.hex
```
