Documentation missing `-f` option for docker-compose up

The README is not up to date, since there is only a docker-compose-prod.yml all calls to docker-compose should include the option -f docker-compose-prod.yml or the documentation should state that docker-compose-prod.yml should be renamed/copied to docker-compose.yml.

The documentation on https://materialdigital.github.io/pmd-server/pages/services/onto-docker/ has the same issue.