Add docker workflow

.github/workflows/docker.yml

@@ -0,0 +1,31 @@
+name: Docker
+
+on:
+  pull_request:
+
+  release:
+    types: [published]
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    steps:
+      # Only log in if we're going to push
+      - if: ${{ github.event_name == 'release' }}
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_PASSWORD }}
+
+      - id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: restyled-io/restylers-whitespace
+
+      - uses: docker/build-push-action@v6
+        with:
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          push: ${{ github.event_name == 'release' }}