wrong volume information in documentation

[fchyzak]

Installing according to II. Without docker-compose in docker/README.md fails to start the application.
It turns out that the list of volumes given for the command line docker run ... in that section of the documentation is inconsistent with the file docker/docker-compose/pigallery2-only/docker-compose.yml.
Instead of -v <path to your db file folder>:/app/data/db \, it should be -v db-data:/app/data/db \.
The application started after I changed the specification of this volume.

The same file docker-compose.yml proposes to suffix :ro in the images volume description.
Without it, the application starts, but it feels safer to have it in the docker run ... command line as well
and I would suggest to have it in the documentation.
I haven't seen if it should work without :ro, but it does.
I haven't found what functionality could be lost with it.

Browser and server on two Linux machines, using Firefox, running edge-debian-bookworm.