Mark action as deprecated and link to replacement

Updated README to indicate deprecation of the action in favor of a new version.

Author: hesreallyhim

README.md

@@ -1,5 +1,7 @@
 <div align="center">
 
+<h1><strong>DEPRECATED: This action is no longer maintained, and has been deprecated in favor of <a href="https://github.com/marketplace/actions/github-api-usage-monitor">github-api-usage-monitor</a>, a more sophisticated and accurate version of this project.</strong></h1>
+
 <img src="assets/header-banner-v2.svg" alt="GitHub API Usage Tracker" width="700"/>
 
 [![GitHub Actions](https://img.shields.io/badge/GitHub-Action-2088FF?style=for-the-badge&logo=github-actions&logoColor=white)](https://github.com/features/actions)