message: Show additional guide message when user types unsupported command
diff: @@ -72,7 +72,8 @@ where
  let command = match Command::parse(line.as_str()) {
  Ok(command) => command,
  Err(_) => {
  - println!("[error] unsupported command: {}", line);
  + println!("[error] command not supported: {}", line);
  + println!("\n type .help to list all available commands.\n");
  continue;
  }
  };
  