code: func (material *Material) AddNews(articles []*Article) (mediaID string, err error) {
  	req := &reqArticles{articles}
  
  	var accessToken string
  	accessToken, err = material.GetAccessToken()
  	if err != nil {
  		return
  	}
  
  	uri := fmt.Sprintf("%s?access_token=%s", addNewsURL, accessToken)
  	responseBytes, err := util.PostJSON(uri, req)
  	var res resArticles
  	err = json.Unmarshal(responseBytes, res)
  	if err != nil {
  		return
  	}
  	mediaID = res.MediaID
  	return
  }
docs: //AddNews 新增永久图文素材