File README.suse-maint.md of Package piper-voices

# Building sources

For the individual language packages, there is `piper-voices-lang.spec.in`.
This is the spec file you should edit if you want to make changes to language
packages. Once done, run:

```sh
bash prepare_sources.sh
```

This will create the individual spec files for each language and the
corresponding tarballs. Make sure you have `git-lfs` installed.