ci: add workflow

.github/workflows/build.yml

@@ -0,0 +1,32 @@
+name: Build APK
+
+on:
+  push:
+    branches:
+      - '*'
+  pull_request:
+    branches:
+      - '*'
+
+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: 'zulu'
+          cache: 'gradle'
+
+      - name: Build project with Gradle
+        run: chmod +x ./gradlew && ./gradlew app:assembleDebug
+
+      - name: Upload apk as artifact
+        uses: actions/upload-artifact@v2
+        with:
+          name: app
+          path: |
+            app/build/outputs/apk/debug/app-debug.apk