Add working demo image

Author: Igor Mucsicska

README.md

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 This package allows sharing data between components with hooks. In many cases leads to more simple implementation compared to Context API.
 `createSharedState` creates a hook very similar to `useState` but with sync state across hook instances. Setting a value in one component will result re-rendering every component which uses the same hook.
 
+![image](https://user-images.githubusercontent.com/3163392/68551190-7fe32c80-040a-11ea-935c-e390f1121a24.png)
+
 ## Side-by-side comparison with Context API
 
 ![image](https://user-images.githubusercontent.com/3163392/68534701-aedc9e00-0337-11ea-89c3-7eed540f23cd.png)