diff --git a/README.md b/README.md
index 28e5c079..1a2f66dc 100644
--- a/README.md
+++ b/README.md
@@ -21,4 +21,6 @@ An action that simply sends a mail to multiple recipients.
     from: Luke Skywalker # <user@example.com>
     # Optional content type (defaults to text/plain):
     content_type: text/html
+    # Optional single file attachment
+    attach_file: attachments.zip
 ```