Update README.md (#453)

<!-- This is an auto-generated comment: release notes by OSS CodeRabbit
-->
### Summary by CodeRabbit

- Documentation: Added a Discord badge to the README.md file. This new
feature provides users with a direct link to join the project's Discord
server, enhancing community engagement and user support.
<!-- end of auto-generated comment: release notes by OSS CodeRabbit -->

Author: guritfaq

README.md

@@ -1,12 +1,8 @@
 # AI-based PR reviewer and summarizer
 
+[![Discord](https://img.shields.io/badge/Join%20us%20on-Discord-blue?logo=discord&style=flat-square)](https://discord.gg/GsXnASn26c)
 [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
-
-<div>
-    <a href="https://github.com/coderabbitai/ai-pr-reviewer)/commits/main">
-    <img alt="GitHub" src="https://img.shields.io/github/last-commit/coderabbitai/ai-pr-reviewer/main?style=for-the-badge" height="20">
-    </a>
-    </div>
+[![GitHub](https://img.shields.io/github/last-commit/coderabbitai/ai-pr-reviewer/main?style=flat-square)](https://github.com/coderabbitai/ai-pr-reviewer/commits/main)
 
 ## Overview