fix example code in README

README.md

@@ -20,8 +20,8 @@ val inputTopic = ...
 // `inputTopic` is the name of the topic where the maintenance message are
 stored; props is a variable containing properties for the Kafka consumer
 val registry = EffectsRegistry()
-val shutdownEffect = Effect("shutdown", () => sys.exit(0), "shuts down
-application")
+val shutdownEffect = Effect("shutdown", () => sys.exit(0), Some("shuts down
+application"))
 // the `register` method takes a message matcher as well as an instance of the
 `Effect` case class
 registry.register(ShutdownMessage, shutdownEffect)