Added build image action

.github/workflows/main.yml

@@ -0,0 +1,28 @@
+# This is a basic workflow to help you get started with Actions
+
+name: build
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Build and push Docker images
+      uses: docker/build-push-action@v1.1.0
+      with:
+        repository: itzg/minecraft-server
+        username: ${{ secrets.DOCKER_USER }}
+        password: ${{ secrets.DOCKER_PASSWORD }}
+        tag_with_ref: true
+        tag_with_sha: true
+        cache_froms: itzg/minecraft-server:latest
+        add_git_labels: true
+        push: false