Add link to the online version of the modal example

Author: eudoxia0

README.md

@@ -16,6 +16,8 @@ callbacks and event handlers.
 
 ## [Modal][modal]
 
+[Online version](http://tryolabs.github.io/react-examples/modal/)
+
 A reusable modal component.
 
 ## [Drag and Drop][dnd]