code: func (t *Torrent) NewReader() Reader {
  	r := reader{
  		mu:        t.cl.locker(),
  		t:         t,
  		readahead: 5 * 1024 * 1024,
  		length:    *t.length,
  	}
  	t.addReader(&r)
  	return &r
  }
docs: // Returns a Reader bound to the torrent's data. All read calls block until
  // the data requested is actually available.