reset: fix usage

The <tree-ish> parameter is actually optional (see man page).

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

builtin/reset.c

@@ -24,7 +24,7 @@
 
 static const char * const git_reset_usage[] = {
 	N_("git reset [--mixed | --soft | --hard | --merge | --keep] [-q] [<commit>]"),
-	N_("git reset [-q] <tree-ish> [--] <paths>..."),
+	N_("git reset [-q] [<tree-ish>] [--] <paths>..."),
 	N_("git reset --patch [<tree-ish>] [--] [<paths>...]"),
 	NULL
 };