[jnigen] Specify JDK min and max version in README (https://github.com/dart-lang/jnigen/issues/384)

pkgs/jnigen/README.md

diff --git a/pkgs/jnigen/README.md b/pkgs/jnigen/README.md
index c5850b5..eaffeaa 100644
--- a/pkgs/jnigen/README.md
+++ b/pkgs/jnigen/README.md
@@ -154,6 +154,9 @@
 Dart standalone target is supported, but due to some problems with pubspec format, the `dart` command must be from Flutter SDK and not Dart SDK. See [dart-lang/pub#3563](https://github.com/dart-lang/pub/issues/3563).
 
 ### Java tooling
+
+**Use JDK versions 11 to 17. The newer versions will not work because of their lack of [compatibility](https://docs.gradle.org/current/userguide/compatibility.html) with Gradle.**
+
 Along with JDK, maven (`mvn` command) is required. On windows, it can be installed using a package manager such as [chocolatey](https://community.chocolatey.org/packages/maven) or [scoop](https://scoop.sh/#/apps?q=maven).
 
 __On windows, append the path of `jvm.dll` in your JDK installation to PATH.__