readme: added compose command to launch multiple engines

README.md

@@ -17,5 +17,10 @@ or
 $ git clone https://git.hammerle.me/fphammerle/docker-toontown-rewritten
 $ cd docker-toontown-rewritten
 $ xhost +
-$ docker-compose up --build
+$ sudo docker-compose up --build
+```
+
+launch multiple engines:
+```sh
+$ sudo docker-compose up -d --scale toontown_rewritten=3
 ```