Update README.md

Author: eralpkaraduman

README.md

@@ -8,3 +8,5 @@ Jump through between high and low bids at the optimum point, Increase your ROI.
 [Play it here](http://eralpkaraduman.github.io/flappybids/)
 
 Made using [Phaser](https://phaser.io) game engine
+
+To extend the game, please refer to [Phaser 1.1.5 Documentation](https://github.com/photonstorm/phaser/tree/1.1.5/docs)