fix(MOBILE/android): make scripts monorepo compatible (#866)

This diff contains minor changes to make the build scripts in here
compatible with https://github.com/bassosimone/monorepo.

See https://github.com/bassosimone/monorepo/commit/5e4c7973801dbd1a582cd21d5000e09a2ee630a7

MOBILE/android/home

@@ -0,0 +1,30 @@
+#!/bin/bash
+
+set -euo pipefail
+
+nocheck=0
+if [[ $# -eq 1 && $1 == "--no-check" ]]; then
+	nocheck=1
+fi
+
+GOOS=$(go env GOOS)
+case $GOOS in
+linux)
+	__sdk_dir=$HOME/Android/Sdk
+	;;
+darwin)
+	__sdk_dir=$HOME/Library/Android/sdk
+	;;
+*)
+	echo "FATAL: unsupported operating system" 1>&2
+	exit 1
+	;;
+esac
+
+ANDROID_HOME=${ANDROID_HOME:-$__sdk_dir}
+if [[ $nocheck == 0 && ! -d $ANDROID_HOME ]]; then
+	echo "FATAL: expected to find android SDK at $ANDROID_HOME, but found nothing" 1>&2
+	echo "HINT: run ./MOBILE/android/setup to (re)install the SDK" 1>&2
+	exit 1
+fi
+echo $ANDROID_HOME