add: cover img to README

README.md

@@ -1,6 +1,8 @@
 # ChatGPT on WeChat! ![License: ISC](https://img.shields.io/badge/License-ISC-yellow.svg) [![wakatime](https://wakatime.com/badge/user/7d2c2fc8-bd1d-4e1e-bb2b-b49c6120ed53/project/205c561e-69ba-4478-b07f-f5bc7a0ed394.svg)](https://wakatime.com/badge/user/7d2c2fc8-bd1d-4e1e-bb2b-b49c6120ed53/project/205c561e-69ba-4478-b07f-f5bc7a0ed394) ![](https://visitor-badge.glitch.me/badge?page_id=kx-Huang.ChatGPT-on-WeChat&left_color=gray&right_color=blue) <!-- omit in toc -->
 
-Turn your WeChat into a auto-reply bot powered by ChatGPT!
+Turn your WeChat into an auto-reply bot powered by ChatGPT!
+
+![Your Chat Bot in Group Chat!](doc/img/demo.png)
 
 ## Acknowledgement && Features