code: func (m *Main) Notify(notifyURL, dnsAddr string) {
  	m.mu.Lock()
  	m.status.URL = strings.Join(m.peers, ",")
  	if dnsAddr != "" {
  		m.status.DNS = dnsAddr
  	}
  	payload, _ := json.Marshal(m.status)
  	m.mu.Unlock()
  
  	res, err := http.Post(notifyURL, "application/json", bytes.NewReader(payload))
  	if err != nil {
  		m.logger.Printf("failed to notify: %s", err)
  	} else {
  		res.Body.Close()
  	}
  }
docs: // Notify sends a POST to notifyURL to let it know that addr is accessible.