Mark this repository as unmaintained

Prepare to mark this repository as unmaintained, let's see what other Actions we can find that also do this.

README.md

@@ -1,5 +1,21 @@
 # Delete Package Versions
 
+**Please note:** This repository is currently unmaintained by a team of developers at GitHub. The 
+repository is here and you can use it as an example, or in Actions. However please be aware that 
+we are not going to be updating issues or pull requests on this repository.
+
+**Maintained Actions:**
+* [SmartsquareGmbH/delete-old-packages](https://github.com/SmartsquareGmbH/delete-old-packages)
+
+
+To reflect this state we’ve marked this repository as Archived.
+
+If you are having an issue or question about GitHub Actions then please [contact customer support](https://help.github.com/en/articles/about-github-actions#contacting-support).
+
+If you have found a security issue [please submit it here](https://hackerone.com/github).
+
+---
+
 This action deletes versions of a package from [GitHub Packages](https://github.com/features/packages).
 
 ### What It Can Do