Set up continuous build for develop tip with GitHub actions.

.github/workflows/main.yml

@@ -0,0 +1,24 @@
+name: Continuous develop build
+on:
+  push:
+    branches:
+      - develop
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        fetch-depth: 0
+    - name: set up JDK 1.8
+      uses: actions/setup-java@v1
+      with:
+        java-version: 1.8
+    - name: Build with Gradle
+      run: ./gradlew assembleDebug
+    - name: Create release
+      uses: eine/tip@gha-tip
+      with:
+        token: ${{ secrets.GITHUB_TOKEN }}
+        cwd: ${{ github.workspace }}
+        files: app/build/outputs/apk/debug/app-debug.apk