Adds RunKit link.

Author: ryasmi

readme.md

@@ -10,6 +10,8 @@
 npm install --save xapi-validation
 ```
 
+[Try it out on RunKit](https://runkit.com/58834fa5d14b5b0013806bde/5883507a9faa130014213d6a).
+
 ## Why?
 1. Find and return all of the problems with your xAPI statements in one function call.
 2. Conformance tested.