github action to build docker image

.github/workflows/docker.yml

@@ -0,0 +1,39 @@
+name: Publish Docker image
+on:
+    push:
+        branches: [ master, stable, docker ]
+jobs:
+    push_to_registry:
+        name: Push Docker image to Docker Hub
+        runs-on: ubuntu-latest
+        steps:
+            -
+                name: Check out the repo
+                uses: actions/checkout@v2
+            -
+                name: Set Branch Environment
+                run: echo "BRANCH=${GITHUB_REF##*/}" >> $GITHUB_ENV
+            -
+                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: splitbrain
+                    password: ${{ secrets.DOCKERHUB_TOKEN }}
+            -
+                name: Build and push
+                uses: docker/build-push-action@v2
+                with:
+                    context: ./docker
+                    file: ./docker/Dockerfile
+                    platforms: linux/amd64,linux/arm64,linux/386
+                    push: true
+                    tags: splitbrain/dokuwiki:${{ env.BRANCH }}
+                    build-args: |
+                        BRANCH=${{ env.BRANCH }}
+