8024659: Clarify JarFile API

Reviewed-by: mullan, ahgross

jdk/src/share/classes/java/util/jar/JarFile.java

@@ -53,6 +53,13 @@ import sun.misc.SharedSecrets;
  * or method in this class will cause a {@link NullPointerException} to be
  * thrown.
  *
+ * If the verify flag is on when opening a signed jar file, the content of the
+ * file is verified against its signature embedded inside the file. Please note
+ * that the verification process does not include validating the signer's
+ * certificate. A caller should inspect the return value of
+ * {@link JarEntry#getCodeSigners()} to further determine if the signature
+ * can be trusted.
+ *
  * @author  David Connelly
  * @see     Manifest
  * @see     java.util.zip.ZipFile