add docker build workflow (#46)

.github/workflows/docker.yml

@@ -0,0 +1,33 @@
+name: Build Docker
+on:
+  release:
+    types: [published]
+
+jobs:
+  build-and-push-docker:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v2
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v2
+      - name: Login to GitHub Container Registry
+        uses: docker/login-action@v2
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.CR_PAT }}
+      - name: Extract version
+        run: |
+          export VERSION=`node -e "console.log(require('./package').version)"`
+          echo "version=$VERSION" >> $GITHUB_OUTPUT
+        id: extract_version
+      - name: Build and push latest
+        uses: docker/build-push-action@v3
+        with:
+          push: true
+          tags: |
+            ghcr.io/ctfd/tourist:latest
+            ghcr.io/ctfd/tourist:${{ steps.extract_version.outputs.version }}