Update CONTRIBUTING.md

The repository will only accept Alpine applications that make use of the Alpine Package Keeper.

.github/CONTRIBUTING.md

@@ -5,3 +5,5 @@ Everybody is invited and welcome to contribute to Proxmox VE Helper Scripts.
 - Pull requests submitted against [**main**](https://github.com/tteck/Proxmox/tree/main) are meticulously scrutinized, so please do not take it personally if the project maintainer rejects your request. By adhering to the established patterns and conventions throughout the codebase, you greatly increase the likelihood that your changes will get merged into [**main**](https://github.com/tteck/Proxmox/tree/main).
 
 - It is important to stress that complaining about the decision after it has been made is not productive behavior for the pull request submitter. It is crucial for all contributors to respect the decision-making process and collaborate effectively towards achieving the best possible outcome for the project.
+
+- The repository will only accept Alpine applications that make use of the Alpine Package Keeper.