diff --git a/README.md b/README.md
index 0d534d0..c484bb5 100644
--- a/README.md
+++ b/README.md
@@ -156,6 +156,8 @@ $sl-img-border-large:  0 none;
 $sl-iframe-border-small:  0 none;
 $sl-iframe-border-medium: 0 none;
 $sl-iframe-border-large:  0 none;
+
+$add-vendor-prefixes: true !default;
 ```