diff --git a/README.md b/README.md
index d47b172..268f490 100644
--- a/README.md
+++ b/README.md
@@ -4,6 +4,7 @@ Detect duplicated images and gather each group into a unique subfolder.
 ## usage
 ```powershell
 Usage: dupimage [-adhst] ext1 ext2...
+  -D    enable debug-level log output
   -a    action sort
   -d string
         work directory (default "./")