Update README.md

Author: NicoLaval

README.md

@@ -1,5 +1,11 @@
 # Trevas Lab
 
+![Maintenance](https://img.shields.io/badge/maintenance-none-red.svg)
+
+> ⚠️ **This project is no longer maintained.**  
+> As of July 2025, this repository is archived and provided as-is.  
+> No further updates, issues, or pull requests will be accepted.
+
 [![Trevas Lab CI](https://github.com/InseeFrLab/Trevas-Lab/actions/workflows/ci.yml/badge.svg)](https://github.com/InseeFrLab/Trevas-Lab/actions/workflows/ci.yml)
 [![License: MIT](https://img.shields.io/badge/License-MIT-blue.svg)](https://opensource.org/licenses/MIT)