Release Note: JEP 364: ZGC on macOS

The Z Garbage Collector (ZGC) is now available as an experimental feature on macOS. To enable it, use the JVM flags `-XX:+UnlockExperimentalVMOptions -XX:+UseZGC`. See [JEP 364: ZGC on macOS](https://openjdk.java.net/jeps/364) for more information.