Added a calculator usage gif

Author: NikolaBreznjak

README.md

@@ -12,4 +12,8 @@ The step by step tutorial is published and you can, of course, check it out for
 + in the project directory execute `ionic lab` to run the project locally in your browser
 
 ### Demo
-You can check out the live example of this application [here](http://hitman666.github.io/Ionic3_2ndTutorial/).
+You can check out the live example of this application [here](http://hitman666.github.io/Ionic3_2ndTutorial/).
+
+Here's a gif of how it looks/works:
+
+![](calculator.gif)