Add Docker Hub README and description sync to workflow (#10)

Author: Copilot

.github/workflows/docker.yml

@@ -71,3 +71,12 @@ jobs:
             ${{ env.REGISTRY }}/${{ secrets.DOCKERHUB_USERNAME }}/${{ env.IMAGE_NAME }}:${{ github.sha }}
           cache-from: type=gha
           cache-to: type=gha,mode=max
+
+      - name: Update Docker Hub description + short desc
+        uses: peter-evans/dockerhub-description@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+          repository: ${{ secrets.DOCKERHUB_USERNAME }}/${{ env.IMAGE_NAME }}
+          readme-filepath: ./README.md
+          short-description: ${{ github.event.repository.description || '' }}