Update README.md (Added contributing field) (#5144)

README.md

@@ -88,3 +88,8 @@ Haxe   | neko
 3.0.0  | 2.0.0
 3.1.3  | 2.0.0
 3.2.0  | 2.0.0
+
+
+## Contributing
+
+See [CONTRIBUTING.md](CONTRIBUTING.md) for more. Thank you!