eat: example app's readme.md (#1452)

## 📜 Description

- added a `example/README.md` with a `screenshot.png` to help how to run
the example app.

## 💡 Motivation and Context

I was not able to run the example app instinctively:
https://github.com/kirillzyusko/react-native-keyboard-controller/issues/1451

Closes
https://github.com/kirillzyusko/react-native-keyboard-controller/issues/1451

## 📢 Changelog

Just doc.

## 🤔 How Has This Been Tested?

Yes, I managed to read it. XD

## 📸 Screenshots (if appropriate):

<img width="1912" height="782" alt="image"
src="https://github.com/user-attachments/assets/5cc4bf8a-e4cc-499b-bf32-b276caa6813e"
/>

## 📝 Checklist

- [ ] CI successfully passed
- [ ] I added new mocks and corresponding unit-tests if library API was
changed

---------

Co-authored-by: kirillzyusko <zyusko.kirik@gmail.com>