Message about broken Gradle for JDK 16 or 17

Author: BruceEckel

README.md

@@ -6,6 +6,10 @@ If you want to experiment with the code examples from the book [On Java
 These examples are automatically extracted directly from the book. This repository
 includes tests to verify that the code in the book is correct.
 
+> NOTE: Do not attempt to use JDK 16 or greater with gradle. 
+> This produces a `BUG!` message from Gradle, which is broken for those versions.
+> To test new Java features in JDK 16 or 17 you must compile and run those examples by hand.
+
 ## Contents
 
 - [Building From the Command Line: Quick Version](#building-from-the-command-line-quick-version)