code: func (p *Client) Subscribe(c *ble.Characteristic, ind bool, h ble.NotificationHandler) error {
  	p.Lock()
  	defer p.Unlock()
  	if c.CCCD == nil {
  		return fmt.Errorf("CCCD not found")
  	}
  	if ind {
  		return p.setHandlers(c.CCCD.Handle, c.ValueHandle, cccIndicate, h)
  	}
  	return p.setHandlers(c.CCCD.Handle, c.ValueHandle, cccNotify, h)
  }
docs: // Subscribe subscribes to indication (if ind is set true), or notification of a
  // characteristic value. [Vol 3, Part G, 4.10 & 4.11]