code: func (b *Bot) GetFile(file *File) (io.ReadCloser, error) {
  	f, err := b.FileByID(file.FileID)
  	if err != nil {
  		return nil, err
  	}
  
  	url := fmt.Sprintf("%s/file/bot%s/%s",
  		b.URL, b.Token, f.FilePath)
  
  	resp, err := http.Get(url)
  	if err != nil {
  		return nil, err
  	}
  	// set FilePath
  	*file = f
  
  	return resp.Body, nil
  }
docs: // GetFile from Telegram servers