Add warning to stop users from using this old action

README.md

@@ -1,14 +1,7 @@
-<div align="center">
-
-  <img
-    src="https://raw.githubusercontent.com/grafana/k6-action/master/k6.gif"
-    width="600"
-    style="pointer-events: none;" />
-
-  <br />
-  Open source load testing tool and SaaS for ambitious engineering teams.
-
-</div>
+> [!CAUTION]
+> This repository has been archived, and this project has been superseded by two new and more robust Github actions.
+>
+> Use [Setup k6 action](https://github.com/marketplace/actions/setup-grafana-k6) to set up K6 in your pipeline and then use [Run k6 action](https://github.com/marketplace/actions/run-grafana-k6-tests) to execute tests.
 
 ## Get started