How to build the Android app locally

[PeterDaveHello]

Hi @kar,

I'd like to build this app locally to test some changes, but looks like the BUILDING.md doc is still WIP, I searched related issues and saw #684, but looks like it's for an older version. I'm not familiar with the Android ecosystem, tried to use Android Studio to build it but failed in different places, still trying. Do you have any time to provide some details about how to build the app locally? I believe that there'll be very helpful to have more contributors here, thanks!