doc: 完善使用文档

Author: devin

README.rst

@@ -60,7 +60,7 @@
 
 .. code:: python
 
-    from dingtalkchatbot.chatbot import DingtalkChatbot
+    from dingtalkchatbot.chatbot import DingtalkChatbot, ActionCard, CardItem
     # WebHook地址
     webhook = 'https://oapi.dingtalk.com/robot/send?access_token=这里填写自己钉钉群自定义机器人的token'
     secret = 'SEC11b9...这里填写自己的加密设置密钥'  # 可选：创建机器人勾选“加签”选项时使用
@@ -111,7 +111,7 @@
 .. code:: python
 
         # Markdown消息@指定用户
-        xiaoding.send_markdown(title='氧气文字', text='#### 广州天气 @18825166128\n'
+        xiaoding.send_markdown(title='氧气文字', text='#### 广州天气 @1882516xxxx\n'
                                '> 9度，西北风1级，空气良89，相对温度73%\n\n'
                                '> ![美景](http://www.sinaimg.cn/dy/slidenews/5_img/2013_28/453_28488_469248.jpg)\n'
                                '> ###### 10点20分发布 [天气](http://www.thinkpage.cn/) \n',

dingtalkchatbot/chatbot.py

@@ -90,9 +90,9 @@ def update_webhook(self):
 
         sign = quote_plus(base64.b64encode(hmac_code))
         if 'timestamp'in self.webhook:
-            self.webhook = '{}&timestamp={}&sign={}'.format(self.webhook[:self.webhook.find('&timestamp')], str(timestamp), sign)
+            self.webhook = '{}&timestamp={}&sign={}'.format(self.webhook[:self.webhook.find('&timestamp')], str(timestamp), sign)  # 更新时间戳
         else:
-            self.webhook = '{}&timestamp={}&sign={}'.format(self.webhook, str(timestamp), sign)
+            self.webhook = '{}&timestamp={}&sign={}'.format(self.webhook, str(timestamp), sign)  # 首次初始化
 
     def msg_open_type(self, url):
         """