docs: end of life

README.md

 # simplesamlphp-module-attribute_check
 
+![maintenance status: end of life](https://img.shields.io/maintenance/end%20of%20life/2024)
+
+This project has reached end of life, which means no new features will be added. Security patches and important bug fixes will end as of 2024. Check out [Apereo CAS](https://apereo.github.io/cas/) or [eduGAIN Access Check](https://access-check.edugain.org/) instead.
+
+## Description
+
 SimpleSAMLphp module for deploying an SP serving as an attribute check.
 
 ## Configuration