Add usage string to git-update-index
Add usage string to git-update-index

This patch adds usage string to git-update-index, can be printed by the -h
or --help parameter.

Signed-off-by: Petr Baudis <2df6472652419df7dced808d07835f28963a653f@suse.cz>
Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git