add warning to readme

README.md

@@ -7,6 +7,12 @@
 [![GitHub Release](https://img.shields.io/github/v/release/wg-easy/wg-easy)](https://github.com/wg-easy/wg-easy/releases/latest)
 [![Image Pulls](https://img.shields.io/badge/image_pulls-11M-blue)](https://github.com/wg-easy/wg-easy/pkgs/container/wg-easy)
 
+<!-- TODO: remove after release -->
+
+> [!WARNING]
+> You are viewing the README of the pre-release of v15.
+> If you want to setup wg-easy right now. Read the README in the production branch here: [README](https://github.com/wg-easy/wg-easy/tree/production) or here for the last nightly: [README](https://github.com/wg-easy/wg-easy/tree/c6dce0f6fb2e28e7e40ddac1498bd67e9bb17cba)
+
 You have found the easiest way to install & manage WireGuard on any Linux host!
 
 <!-- TOOD: update screenshot -->