add docker workflow

.github/workflows/docker.yml

@@ -0,0 +1,29 @@
+name: Docker Image
+
+on:
+  push:
+    # Sequence of patterns matched against refs/tags
+    tags:
+    - "v*" # Push events to matching v*, i.e. v1.0, v20.15.10
+    branches:
+    - 'master'
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Set up QEMU
+      uses: docker/setup-qemu-action@v1
+    - name: Set up Docker Buildx
+      uses: docker/setup-buildx-action@v1
+    - name: Login to DockerHub
+      uses: docker/login-action@v1
+      with:
+        username: ${{ secrets.DOCKERHUB_USERNAME }}
+        password: ${{ secrets.DOCKERHUB_TOKEN }}
+    - name: Build and push
+      id: docker_build
+      uses: docker/build-push-action@v2
+      with:
+        push: true
+        tags: user/app:latest