Add GitHub Actions workflow

.github/workflows/android.yml

@@ -0,0 +1,34 @@
+name: Android CI
+
+on:
+  push:
+    branches: [ dev ]
+  pull_request:
+    branches: [ dev ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: set up JDK 11
+      uses: actions/setup-java@v2
+      with:
+        java-version: '11'
+        distribution: 'temurin'
+        cache: gradle
+
+    - name: Generate temporary keystore
+      run: keytool -genkey -v -storetype pkcs12 -keystore store.p12 -storepass android -alias android -keyalg RSA -keysize 2048 -validity 10000 -dname CN=CI
+    - name: Write retro.properties
+      run: |
+        cat >retro.properties <<EOF
+        storeFile=$PWD/store.p12
+        keyAlias=android
+        storePassword=android
+        keyPassword=android
+        EOF
+    - name: Build with Gradle
+      run: ./gradlew build