Update README.md

Author: cheesytim

README.md

@@ -5,4 +5,6 @@ based on [google-map-react](https://github.com/istarkov/google-map-react) (witho
 
 ### [Demo](https://tim152.github.io/clustering-google-map-react/)
 
+![clustering google map react](https://github.com/Tim152/clustering-google-map-react/blob/master/public/demo.png)
+
 This project was bootstrapped with [Create React App](https://github.com/facebookincubator/create-react-app).