Add github action to automatically build docker images

.github/workflows/docker.yml

@@ -0,0 +1,27 @@
+name: Build and push Docker images
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    - steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Build dev image
+        uses: docker/build-push-action@v1
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+          cache_froms: wger/base:2.0-dev
+          repository: wger/devel
+          dockerfile: extras/docker/development/Dockerfile
+          tags: latest,2.0-dev
+          tag_with_ref: true