docs: update readme to inform on repo move

Author: nexus49

README.md

@@ -1,5 +1,5 @@
 > [!WARNING]
-> This Repository is under development and not ready for productive use. It is in an alpha stage. That means APIs and concepts may change on short notice including breaking changes or complete removal of apis.
+> This Repository was moved to https://github.com/platform-mesh/extension-manager-operator
 
 # OpenMFP - Extension Manager Operator