Fix relative path for image to properly show on Pub

Author: jesusbibieca

example/README.md

@@ -7,7 +7,7 @@ This exmaple shows four carousel slider examples:
 - Image slider with full width display
 - Image slider with indicator
 
-![screenshot](./demo_screenshot.png)
+![screenshot](https://github.com/serenader2014/flutter_carousel_slider/blob/master/example/demo_screenshot.png)
 
 # Running