Add Citation File Format file format

Add a `CITATION.cff` file in order that other researchers or other type of users can cite this software. The [specification](https://citation-file-format.github.io/) is encoded in YAML.


Github in the UI will show a dialog with the corresponding formated citation:

<img width="562" height="368" alt="Image" src="https://github.com/user-attachments/assets/e58f073f-6313-407f-a510-ab6b75f90fd0" />