docs: private static void usage(PrintStream s) {
      s.println("usage: Client [options] <torrent>");
      s.println();
      s.println("Available options:");
      s.println("  -h,--help                  Show this help and exit.");
      s.println("  -o,--output DIR            Read/write data to directory DIR.");
      s.println("  -i,--iface IFACE           Bind to interface IFACE.");
      s.println("  -s,--seed SECONDS          Time to seed after downloading (default: infinitely).");
      s.println("  -d,--max-download KB/SEC   Max download rate (default: unlimited).");
      s.println("  -u,--max-upload KB/SEC     Max upload rate (default: unlimited).");
      s.println();
    }