Updated 在线授课接口定义 (markdown)

@@ -67,6 +67,7 @@ Request Method： GET
 
 ```json
 {
+    "type": "ONLINE_TEACH",
     "teacher_info": {
         "figure_url": "http://wx.qlogo.cn/mmopen/PiajxSqBRaEJrztQnGAk8X1G2A0AfjvPRBdgLFOjxsM9AoicoOUrH3Yia3qY9uic5ibQO6wMkJ6bPUx15IN4Vrxv8CA/0",
         "teacher_name": "喜洋洋老师"
@@ -75,4 +76,7 @@ Request Method： GET
     "group_id": "@TGS#2AA4BQAEN",
     "chat_room_id": "100001"
 }
-```
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+```
+
+说明： type 的类型为 *ONLINE_TEACH* 和 *MESSAGE* 
+*ONLINE_TEACH* 为教学相关，*MESSAGE* 正常显示
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