Document how to get debug output

README.md

@@ -19,3 +19,12 @@ Options:
       --baud-rate <BAUD_RATE>  Baud rate used for connecting to the serial device [default: 115200]
   -h, --help                   Print help
 ```
+
+## Debug
+
+This software uses [Rusts `env_logger` crate](https://docs.rs/env_logger/latest/env_logger/) for debugging.
+Enable debug output to print a whole dump of all communication through the serial interface.
+
+```
+RUST_LOG=debug improv-setup
+```