Hedgedoc does not provide database in examples

[mattnukem]

https://docs.linuxserver.io/images/docker-hedgedoc/

For convenience we provide a working example using Mariadb as a backend in this document.

No database config is provided in either the docker compose or docker run examples that follow. This seems to be an oversight, as these examples will not function without either running a separate database or adding one to the Hedgedoc config.