Update docker-compose.yml

[joergmschulz]

enable rootless design

[grnd-alt]

@joergmschulz thanks for your pr. I am not entirely sure why this is needed, though I am not familiar with the rootless docker mode. Could you please elaborate why the files would not be writable in rootless mode? I would've expected that all files inside of the container are still accessible by the node process.

[joergmschulz]

the issue is: when I create a container that runs the server app as a non-root user (name him whiteboard) while leaving the files in the whiteboard app directory owned by root, the whiteboard user cannot create the backup directory. This prevents the start of the server.