readme: add disclaimer about project not being maintained

Author: marquiz

README.md

@@ -1,6 +1,15 @@
 # CRI Resource Manager for Kubernetes\*
 
-Welcome!
+## ⚠️ The project is no longer maintained ⚠️
+
+The CRI Resource manager project is no longer maintained. No further updates,
+bug fixes or releases are planned.
+
+We recommend users migrate to
+[NRI Plugins](https://github.com/containers/nri-plugins), which provides
+similar functionality and is actively maintained.
+
+Thank you for being part of this journey!
 
 ### See our [Documentation][documentation] site for detailed documentation.