Update README.md (#800)

README.md

@@ -43,11 +43,12 @@ It's important to note that Open-IM-Server isn't a standalone product, and it do
 
 <div align="center">
 
+
 |                    multiple message                     |                     Efficient meetings                      |
-| :------------------------: | :--------------------------------: |
-|    ![](./docs/images/)     |        ![](./docs/images/)         |
+| :-----------------------------------------------------: | :---------------------------------------------------------: |
+| ![multiple-message](./assets/demo/multiple-message.png) | ![efficient-meetings](./assets/demo/efficient-meetings.png) |
 |             **One-to-one and group chats**              |           **Special features - Custom messages**            |
-|    ![](./docs/images/)     |        ![](./docs/images/)         |
+|       ![group-chat](./assets/demo/group-chat.png)       |   ![special-function](./assets/demo/special-function.md)    |
 
 </div>