Add docker build (#1239)

.github/workflows/docker.yml

@@ -0,0 +1,19 @@
+name: Docker
+
+on:
+  push:
+    branches:
+    - master
+
+jobs:
+  build:
+     runs-on: ubuntu-latest
+     steps:
+       - uses: actions/checkout@v2
+         name: Check out repository
+       - uses: elgohr/Publish-Docker-Github-Action@2.12
+         name: Build and Push Docker Image
+         with:
+           name: micro/go-micro
+           username: ${{ secrets.DOCKER_USERNAME }}
+           password: ${{ secrets.DOCKER_PASSWORD }}