Add default `config.json` to git

[Zabuzard]

Right now, users are expected to read our tutorial (Wiki) and copy the example config.json given there into their code base for the project to work.

This is easy to miss for users. And hard to maintain for us (it got outdated several times already).

Instead, the code should either generate it on-the-fly (using code or build scripts) or we simply add the config.json to git. This was not done originally, since local changes should not be tracked by git on user end - users should not push in changes to the file accidentally.

A solution to this might actually be:
https://stackoverflow.com/questions/9794931/keep-file-in-a-git-repo-but-dont-track-changes

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 5 days.

[Zabuzard]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 5 days.

This is actually still relevant, we need it eventually.

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 5 days.