add action to delpoy docker image to dockerhub (#51)

.github/workflows/docker-image.yml

@@ -0,0 +1,20 @@
+name: Publish to DockerHub
+on:    
+  release:
+      types: [published]
+  push:
+    branches:
+      - master
+jobs:
+  update:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+    - name: Publish to Registry
+      pre: echo ::save-state name=RELEASE_VERSION::$(echo ${GITHUB_REF:10})
+      uses: elgohr/Publish-Docker-Github-Action@master
+      with:
+        name: taylorbourne/xteve_lazystream
+        username: ${{ secrets.DOCKER_USERNAME }}
+        password: ${{ secrets.DOCKER_PASSWORD }}
+        tags: "latest,${{ env.STATE_RELEASE_VERSION }}"