Add app icon to the README file

README.md

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+<img alt="SlidingPuzzle icon" src="https://github.com/andremion/SlidingPuzzle/blob/main/androidApp/src/main/res/mipmap-xxxhdpi/ic_launcher.webp" width=100 align=left>
+
 <a target=_blank href='https://play.google.com/store/apps/details?id=io.github.andremion.slidingpuzzle.android'><img alt='Get it on Google Play' src='https://play.google.com/intl/en_us/badges/static/images/badges/en_badge_web_generic.png' height=48 align=right /></a>
 
+</br>
+
 # Sliding-Puzzle Game
 
 A Kotlin multiplatform puzzle game based on the [Sliding-Puzzle](https://en.wikipedia.org/wiki/15_puzzle) problem that uses [A* search algorithm](https://en.wikipedia.org/wiki/A*_search_algorithm) to solve it.