Document how to load sample data

[tacman]

Is your feature request related to a problem? Please describe.

My installation is empty, I'd like some sample data.

Describe the solution you'd like

The doctrine migrations add data for MySQL only, I think. I'm using sqlite.

Describe alternatives you've considered

What I'd like to do is export the data from the public demo site and import it locally. But I can't find the links to do that. I imagine

bin/console partsdb:backup

if that file or a zipped version were available in the repo or somewhere else, then presumably there's an restore command.

bin/console partsdb:restore my-backup-file.zip

This is really a cool project, I'm inspired to add some of these features to my own projects. My initial interest was just seeing how this integrated with settings-bundle, but really there's a lot of great stuff, like 2fa and saml-signon and api integrations.