Warn on breaking changes

Change-Id: I968ab4eeed723d494ddea4fb0ebbd32a48797171
diff --git a/README.md b/README.md
index fa06df1..398a0c1 100644
--- a/README.md
+++ b/README.md
@@ -9,6 +9,8 @@
 `Kalamar-Plugin-ExternalResources` is meant to be a basic plugin and should
 demonstrate and evaluate the plugin capabilities of Kalamar.
 
+**This is software in an early development stage. Its behaviour may change without warnings!**
+
 ## Prerequisites
 
 Go 1.19 or later