Merge pull request #3842 from batmat/document-java-version

Give more details about the expected Java version format

core/src/main/java/jenkins/util/java/JavaUtils.java

@@ -65,6 +65,12 @@ public class JavaUtils {
 
     /**
      * Returns the JVM's current version as a {@link String}.
+     * See https://openjdk.java.net/jeps/223 for the expected format.
+     * <ul>
+     *     <li>Until Java 8 included, the expected format should be starting with <code>1.x</code></li>
+     *     <li>Starting with Java 9, cf. JEP-223 linked above, the version got simplified in 9.x, 10.x, etc.</li>
+     * </ul>
+     *
      * @see System#getProperty(String)
      */
     public static String getCurrentRuntimeJavaVersion() {