Build docker images on merge into master (#29)

* Build docker images on merge into master

* Add username and password to login in docker hub

.github/workflows/dockerimage.yml

@@ -0,0 +1,20 @@
+name: Docker Image CI
+
+on:
+  push:
+    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:
+        username: ${{ secrets.DOCKER_USERNAME }}
+        password: ${{ secrets.DOCKER_PASSWORD }}
+        repository: caddy/ingress
+        tag_with_ref: true
+        tag_with_sha: true