Setup GitHub Actions CI workflow

.github/workflows/gradle-ci.yml

@@ -0,0 +1,22 @@
+name: Gradle CI
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Initialize JDK 16
+        uses: actions/setup-java@v2
+        with:
+          java-version: '16'
+          distribution: 'adopt'
+
+      - name: Build with Gradle
+        uses: burrunan/gradle-cache-action@v1
+        with:
+          arguments: build --stacktrace