chore: build and push image on release (#5)

.github/workflows/release.yml

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+name: Build and push Docker image when a release is published
+
+on:
+  release:
+    types: [published]
+
+jobs:
+  build:
+    name: Build and push Docker image
+    runs-on: ubuntu-latest
+
+    permissions:
+      contents: read
+      packages: write
+
+    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: Log in to Docker registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Extract metadata (tags, labels) for Docker
+        id: meta
+        uses: docker/metadata-action@v4
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+
+      - name: Extract GUI version
+        id: gui
+        env:
+          TAGS: ${{ steps.meta.outputs.tags }}
+        run: echo "::set-output name=version::${TAGS##*:}"
+
+      - name: Build and push Docker image
+        uses: docker/build-push-action@v3
+        with:
+          context: .
+          push: true
+          build-args: |
+            GUI_VERSION=${{ steps.gui.outputs.version }}
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          platforms: linux/amd64,linux/arm64

RELEASE.md

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+To build and publish a release of the official Docker image, in this example patch version `v1.0.1`:
+
+1. Create a tag with name `v1.0.1`
+
+```
+% git tag v1.0.1
+```
+
+2. Push the tag to GitHub remote
+
+```
+% git push --tags
+```
+
+3. Open browser and navigate to the repository on GitHub. Go to the Releases section by clicking on the Releases header on the right side of the page.
+
+4. Click on Create a new release and choose the tag `v1.0.1` that you created.
+
+5. Describe the release by adding release notes in the markdown input field.
+
+6. Click on Publish release.
+
+This will trigger a GitHub action that will build Docker image and tag it with `v1.0.1` and push to container registry.