docs: private static void usage(PrintStream s) {
  		s.println("usage: Tracker [options] [directory]");
  		s.println();
  		s.println("Available options:");
  		s.println("  -h,--help             Show this help and exit.");
  		s.println("  -p,--port PORT        Bind to port PORT.");
  		s.println();
  	}