docker-compose: added comment how to increase verbosity of libgl

docker-compose.yml

@@ -12,6 +12,7 @@ services:
     image: fphammerle/toontown-rewritten
     environment:
     - DISPLAY
+    #- LIBGL_DEBUG=verbose
     volumes:
     - /tmp/.X11-unix:/tmp/.X11-unix:ro
     - engine:/toontown-rewritten/engine:rw