Added a contributing section.

Pull requests are welcome...

README.md

@@ -173,3 +173,12 @@ An application can only display one notification at a time. Each time a new noti
 
 ### Canceling a notification under WP8
 The methods `cancel` and `cancelAll` have the same effect.
+
+
+## Contributing
+
+1. Fork it
+2. Create your feature branch (`git checkout -b my-new-feature`)
+3. Commit your changes (`git commit -am 'Add some feature'`)
+4. Push to the branch (`git push origin my-new-feature`)
+5. Create new Pull Request