Update CITATION.cff to use preferred-citation

[BenjaminRodenberg]

• Use preferred-citation to point to the FEniCS-preCICE paper
• Provide citation information about software on top level.
  • Open for discussion: Might be extended with other/future contributors that did not author the paper. Important: We need a proper and simple policy here. See also https://github.com/precice/fenics-adapter/graphs/contributors
  • Add a DOI? We could point to the preCICE distribution, but this is actually a superset of FEniCS-preCICE and the policy w.r.t. authorship is also independent. I would rather keep things separate and not provide a DOI. If we really want a DOI, we can still release on zenodo. This looks to me like the go-to-solution suggested by the CFF developers: https://citation-file-format.github.io/

[BenjaminRodenberg]

@richahert

[ajaust]

Thanks for updating the citation information.

Should the discussion about the DOI and future authors be in separate issues?

When going through the repository I found another point that should potentially be discussed: Where/How do we want to maintain the citation information of the FEniCS adapter.

Currently, we have to maintain three places:

1. This CITATION.cff file.

   The file and citation mechanism might be new to many people so we might need to explicitly mention GitHub's citation mechanism somewhere.

2. There is a citation section in the README.

3. There is a section on the adapter website that is part of the project.