Improve add usage message.
diff --git a/regress/modify.c b/regress/modify.c
index 5cd3e4a..757b4b5 100644
--- a/regress/modify.c
+++ b/regress/modify.c
@@ -50,7 +50,7 @@
     "\nSupported commands and arguments are:\n"
     "\tadd name content\n"
     "\tadd_dir name\n"
-    "\tadd_file name filename offset len\n"
+    "\tadd_file name file_to_add offset len\n"
     "\tadd_from_zip name archivename index offset len\n"
     "\tdelete index\n"
     "\tget_archive_comment\n"