Update md file by adding a simple example

[EZZAHED]

the example is copied form here https://github.com/final-form/react-final-form-hooks

[codesandbox-ci[bot]]

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Sandbox	Source
React Final Form - Simple Example	Configuration
React Final Form - Synchronous Record Level Validation	Configuration
React Final Form - Synchronous Field Level Validation	Configuration
React Final Form - Submission Errors	Configuration
React Final Form - Subscriptions Example	Configuration

[mrfratello]

This example is not suitable, since the hooks are taken from 'react-final-form-hooks'. It uses another api