File PACKAGING_README.md of Package nix-installer

# Packaging nix-installer

In addition to the source code in the tarball, this package also
needs the nix tarballs for all supported architectures.
The `Makefile` that is present in this package makes the
preparation easier.

To do that, you need to have `make` and the OBS services `obs-service-tar_scm`,
`obs-service-set_version`, `obs-service-download_files` and `obs-service-cargo`
installed locally.

1. Change the version in the `_service` file
2. Run `make`
3. Check the changelog entry that was automatically created
4. Commit the changes as usual