fix 'got tree' usage message; the path argument is optional
diff --git a/got/got.c b/got/got.c
index fa1572e..e8ed834 100644
--- a/got/got.c
+++ b/got/got.c
@@ -4294,7 +4294,7 @@ __dead static void
usage_tree(void)
{
fprintf(stderr,
- "usage: %s tree [-c commit] [-r repository-path] [-iR] path\n",
+ "usage: %s tree [-c commit] [-r repository-path] [-iR] [path]\n",
getprogname());
exit(1);
}