Correct help in webosvbox script

Update the help text to reflect the command name change from "launch" to
"start".

Open-webOS-DCO-1.0-Signed-off-by: Keith Derrick <keith.derrick@palm.com>

Change-Id: I502080421806871ea931689af920803bd340603a
Reviewed-on: http://g2g.palm.com/1393
Reviewed-by: Keith Derrick <keith.derrick@palm.com>
Tested-by: Keith Derrick <keith.derrick@palm.com>