Update the git-ls-tree documentation

Update the git-ls-tree documentation

This patch aims to freshen up a bit the git-ls-tree documentation. It hints
that the list of paths are in fact patterns to be matched, explains the new
-t, --name-only and --name-status options, corrects the original autorship
information to refer to yours sincerely, corrects several grammar mistakes,
etc.

Since the documentation still deserves some significant work (at least
proper description of the pattern matching), I also added the stub notice.

Signed-off-by: Petr Baudis <pasky@suse.cz>
Signed-off-by: Junio C Hamano <junkio@cox.net>