Add CITATION.cff

[gonzalocasas]

Github now supports the new CITATION.cff file format, we should add one and update the bibtex in the docs to match.

• More info: citation files
• Example: CITATION.cff for COMPAS RRC

[jf---]

@gonzalocasas makes sense and included in the documentation

@misc{compas-dev,
title = {{COMPAS}: A framework for computational research in architecture and structures.},
author = {Tom Van Mele and many others},
note = {http://compas.dev},
year = {2017-2021},
doi = {10.5281/zenodo.2594510},
url = {https://doi.org/10.5281/zenodo.2594510},
}