diff --git a/README.md b/README.md
index 585a023..e71b0c2 100644
--- a/README.md
+++ b/README.md
@@ -23,6 +23,7 @@ Make sure you have them all installed.
 * inkscape
 * GNU parallel
 * bash
+* optipng
 
 ```
 # clone this repo and enter to it