Update the JMC options on the man page

In JMC 6.0.0, bundled with JDK 9,
we have changed the default behavior when setting vmargs for JMC.

The options should change from:

-vmargs <jvm-arguments>
Override the jvm arguments specified in the jmc.ini file located in JDK/bin

--launcher.appendVmargs
Append jvm arguments to the -vmargs flag to those in the jmc.ini file.



to:

-vmargs <jvm-arguments>
Append <jvm-arguments> to the the jvm arguments specified in the jmc.ini file located in JDK/bin

--launcher.overrideVmargs
Override the jvm arguments from the jmc.ini file with those specified with the -vmargs flag.