add env 'DOCKER_VOLUME_STORAGE' for volume path customization

examples/flame/docker-compose.yml

@@ -5,7 +5,7 @@ services:
     image: pawelmalak/flame
     container_name: flame
     volumes:
-      - /mnt/docker-volumes/flame:/app/data
+      - ${DOCKER_VOLUME_STORAGE:-/mnt/docker-volumes}/flame:/app/data
       #- /var/run/docker.sock:/var/run/docker.sock # optional but required for Docker integration
     ports:
       - 5005:5005