docs(docker): add docker-compose sample

docker-compose.yml

@@ -0,0 +1,16 @@
+version: "3.9"
+
+services:
+  ondemand:
+    image: gchr.io/acouvreur/traefik-ondemand-service:latest
+    command:
+      - --swarmMode=true
+    volumes:
+      - /var/run/docker.sock:/var/run/docker.sock:ro
+    networks:
+      - traefik
+
+networks:
+  traefik:
+    external: true
+    name: traefik