code: public void trackers(List<String> value) {
          string_vector v = new string_vector();
  
          for (String s : value) {
              v.push_back(s);
          }
  
          p.set_trackers(v);
      }
docs: If the torrent doesn't have a tracker, but relies on the DHT to find
  peers, this method can specify tracker URLs for the torrent.
  
  @param value the list of trackers