one exists for package loader [1].

We should have a dedicated section on how to run a new dvcs loader somewhere in our
documentation.

Either add a section to the existing vcs loader overview [2]. Or create a full new
howto.

This should detail how to mount local overrides within the least required amount of
services (so that even save code now works with the new type for example).

[1] https://docs.softwareheritage.org/devel/swh-loader-core/package-loader-tutorial.html?highlight=run#running-your-loader

[2] https://docs.softwareheritage.org/devel/swh-loader-core/vcs-loader-overview.html