add badges for textbook repo

README.md

@@ -1,9 +1,20 @@
-# XJTU-ICS Textbook
+<h1 align="center">
+    XJTU-ICS Textbook
+</h1>
 
-This is the official website for XJTU-ICS textbook :wave:
+<p align="center">
+    <!-- use https://shields.io/badges/git-hub-contributors -->
+    <img alt="GitHub contributors" src="https://img.shields.io/github/contributors/xjtu-ics/textbook">
+    <!-- use https://shields.io/badges/git-hub-actions-workflow-status -->
+    <img alt="GitHub Actions Workflow Status" src="https://img.shields.io/github/actions/workflow/status/xjtu-ics/textbook/mdbook.yml">
+    <!-- use https://shields.io/badges/git-hub-license -->
+    <img alt="GitHub License" src="https://img.shields.io/github/license/xjtu-ics/textbook">
+    <!-- use https://shields.io/badges/git-hub-repo-stars -->
+    <img alt="GitHub Repo stars" src="https://img.shields.io/github/stars/xjtu-ics/textbook">
+</p>
 
 - How to contribute
-    - [TA's Tutorial](https://blog.bxhu2004.com/BLOG/Markdown/mdbook-site/)
+    - [A Tutorial on mdBook](https://blog.bxhu2004.com/BLOG/Markdown/mdbook-site/)
     - [Inspiration](./ref-template.md)
 - Acknowledgement
     - [Template](https://github.com/lzzsG/mdBook-pages-template)