I wonder whether it's not mentioned in the docs on purpose. The SQLite is present as an option, but only seems to be meant to be used for development, not when you're actually running the server in production. I guess you could start the container, then look into its file system to find the DB location and map it where you want it. (Sorry I can't tell you exactly - I have never tried. By a quick glance at the source, you're probably looking for one of these file names. Maybe search for *.sqlite?)
I'm also curious to know whether someone is actually running it like this in prod? I wouldn't, but maybe someone does?