Hi, there are now nightly builds for the Android app: https://download.delta.chat/android/nightly/
Each night, the current state of the master branch is built, so you can follow the development progress.
It would be cool to have an apk for each pull request, as with the Desktop Client, but unfortunately building the Android app once takes about 23 minutes, which would be worse if there were multiple concurrent Android builds. So @link2xt and I decided for nightly builds instead.
Have fun developing