diff --git a/README.md b/README.md
index cd6e0929..90013e41 100644
--- a/README.md
+++ b/README.md
@@ -19,4 +19,6 @@ An action that simply sends a mail to multiple recipients.
     body: file://README.md
     to: obiwan@tatooine.com,yoda@dagobah.com
     from: Luke Skywalker
+    # Optional content type:
+    content_type: text/html
 ```