RFR 8225561: jlink --help doesn't state that ALL-MODULE-PATH is accepted for --add-modules

[sundararajan . athijegannathan]

Please review.

Bug: https://bugs.openjdk.java.net/browse/JDK-8225561

Webrev: http://cr.openjdk.java.net/~sundar/8225561/webrev.00/

Thanks

-Sundar