add run-once option help message

other/websockify.c

@@ -35,6 +35,7 @@ char USAGE[] = "Usage: [options] " \
                "[source_addr:]source_port target_addr:target_port\n\n" \
                "  --verbose|-v       verbose messages and per frame traffic\n" \
                "  --daemon|-D        become a daemon (background process)\n" \
+               "  --run-once         handle a single WebSocket connection and exit\n" \
                "  --cert CERT        SSL certificate file\n" \
                "  --key KEY          SSL key file (if separate from cert)\n" \
                "  --ssl-only         disallow non-encrypted connections";