Update README.md

Author: yoshimkd

README.md

@@ -1,2 +1,5 @@
 # swift-event-handler-usage-demo
 A simple demo iOS application demonstrating the usage of the SwiftEventHandler framework.
+
+When tapping on the `Add` button, a new row with the next highest number is inserted at a random position.
+When tapping on the `Remove` button, a row is deleted at a random position.