Add note about usage in App Store listing

[mlnchk]

Why

Hi! First of all, thanks for your work. I'm a huge fan of Expo.

I wanted to use react-native-dynamic-app-icon for creating icon A/B testing in my App Store listing, but, unfortunately, this package doesn't add icons as .appiconset, which is required for App Store Connect. So I've created another config plugin to make it possible. I thought it would be useful to add a reference for those who were searching like me.

Not intended as self-promotion :)