Add a GitHub action for Android build

.github/workflows/main.yml

@@ -0,0 +1,23 @@
+# This is a basic workflow to help you get started with Actions
+
+name: Android Build
+
+# Controls when the action will run. 
+on:
+  # Triggers the workflow on push or pull request events but only for the master branch
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+  # Allows you to run this workflow manually from the Actions tab
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout the code
+        uses: actions/checkout@v2
+      - name: Build the app
+        run: cd ExampleProject/ && ./gradlew build