Add basic github actions

.github/workflows/build.yml

@@ -0,0 +1,12 @@
+name: Build
+on: [push, pull_request]
+jobs:
+  build:
+    runs-on: ubuntu-20.04
+    container:
+      image: openjdk:14-jdk
+      options: --user root
+    steps:
+      - uses: actions/checkout@v1
+      - uses: gradle/wrapper-validation-action@v1
+      - run: ./gradlew build --stacktrace