This has been removed since it's not actively maintained, and was providing outdated information.
The BookStack project maintains a linuxserver.io based example stack compose config here.
For using with nginx-proxy-manager (to get HTTPS) you could refer to this video here. Note: This is a bit outdated also though, especially for the docker config itself so don't follow that.
If you really want to see the last outdated state of this file, it can be seen here.
this needs another update - see comments below:
I spent an evening trying to track down a bug in this docker_compose.yml file. It looks like linuxserver now requires that the environment configuration use the 'DB_USERNAME' instead of 'DB_USER' and 'DB_PASSWORD' instead of 'DB_PASS'