Update readme

README.md

 # xJava
 
 Exercism Exercises in Java
+
+## Contributing Guide
+
+Please see the [contributing guide](https://github.com/exercism/x-api/blob/master/CONTRIBUTING.md#the-exercise-data)
+
 ## License
+
 The MIT License (MIT)
 
 Copyright (c) 2014 Katrina Owen, _@kytrinyx.com