Add link to uAppExplorer on GitHub repository home

[bittner]

Please add the link you your app on uAppExplorer at https://github.com/SunRain/PhoenixPlayer next to the repo description ("Yet another cross platform music player by Qt/qml") on top of the page.

https://uappexplorer.com/app/phoenixplayer.sunrain

This way people can find screenshots, description, change log and user reviews of the app more easily.