name-rev: split usage string

Give each mode of operation (all, from stdin, given commits) its own usage
line to make it easier to see that they are mutually exclusive.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/name-rev.c

@@ -172,7 +172,9 @@ static void show_name(const struct object *obj,
 }
 
 static char const * const name_rev_usage[] = {
-	"git name-rev [options] ( --all | --stdin | <commit>... )",
+	"git name-rev [options] <commit>...",
+	"git name-rev [options] --all",
+	"git name-rev [options] --stdin",
 	NULL
 };