Gradle is automatically configured by Android Studio. However, the project is troublesome to build when using other tools. Per https://docs.gradle.org/current/userguide/gradle_wrapper.html#sec:adding_wrapper, the files added by this patch ought to be included in the repository

After applying this diff, it should be possible to clone a fresh repository and run ./gradlew build, resulting in an .apk in ./build/outputs/apk/*/