git-gui: Include browser in our usage message.
git-gui: Include browser in our usage message.

Now that the 'browser' subcommand can be used to startup the tree
browser, it should be listed as a possible subcommand option in
our usage message.

Signed-off-by: Shawn O. Pearce <f01032651c12a22b2103346ba96b3b6b231f9d3c@spearce.org>
destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git