Include "config.yaml.dist" to release .tar.gz files

In packaged "README.md":

```
ig-path=path
YAML configuration file. Minimal working configuration in config.yaml.dist. Options passed through command line will override the ones from this file.
```

But there is no " config.yaml.dist" file which is unuseful.

Start with the release packaging workflow (tarball build step in repository scripts, Makefile, or CI config) that defines what goes into the `.tar.gz` files. Confirm where files are copied from and why `config.yaml.dist` is missing compared with the packaged README mention. Add the file to the packaging manifest, then run the release-package/build command to regenerate an archive and verify `config.yaml.dist` appears in it. Done when the generated tarball contains that file and the README reference is no longer broken.

Scritto dal modello di indicizzazione a partire dal testo della issue.