docs: allow to use Docker Compose to render the docs locally

  $ cd docs/
  $ docker compose up

docs/compose.yaml

@@ -0,0 +1,10 @@
+services:
+  docs:
+    image: europe-west3-docker.pkg.dev/zeitonline-engineering/docker-zon/sphinx-zon:latest
+    command: sphinx-autobuild --host localhost /docs /docs/htdocs
+    network_mode: host
+    restart: always
+    volumes:
+      - .:/docs
+networks:
+  default: {}