add README explaining move

Signed-off-by: Jonathan Dowland <[email protected]>

Author: jmtd

README.md

@@ -0,0 +1,9 @@
+# This repository has moved!
+
+The Red Hat OpenJDK container image sources now live at:
+<https://github.com/rh-openjdk/redhat-openjdk-containers>
+
+Please update your references!
+
+*This* repository is a clone created at the time we migrated
+and will steadily go out of date.