Fixed contributing markdown link

Author: philsturgeon

README.md

@@ -91,7 +91,7 @@ API-Flow is one of the main components of [Console.REST](https://github.com/luck
 
 ## Contributing
 
-Read [CONTRIBUTING.md][] for more tips on testing and contributing.
+Read [CONTRIBUTING.md](CONTRIBUTING.md) for more tips on testing and contributing.
 
 Our sole requirement is that organizations that want to extend API-Flow to support their format write both a parser and a serializer, and not simply a serializer.