Add a CITATION.cff

Feature

Add a CITATION.cff file to the root of the repository that contains all the necessary metadata to properly cite mypy.

Pitch

There has been a trend in some scientific communities encouraging proper citation of all tools used to conduct research. While this generally includes research methods, it may also include software tools such as mypy.

However, it can be difficult to know how to properly cite software if the information is not explicitly provided. It is helpful if the software maintainers/developers provide users with this information.

GitHub recommends, and integrates support for, CITATION.cff files. Inclusion of this file would immediately have these benefits:

• Users will have the necessary metadata to properly cite mypy.
• GitHub can automatically generate both APA and BibTeX formatted citations. A "Cite this repository" option will automatically appear on the repo's sidebar when viewed on a desktop browser.
• Reference managers like Zotero will automatically detect the metadata so the user can save the citation to their library.

Examples of popular packages using this are pandas and tensorflow.

I would be happy to create an initial version of this and open a PR if there is interest in possibly merging it after refinement.

Erstelle CITATION.cff im Stammverzeichnis des Repositorys. Beginne damit, die CITATION.cFF-Richtlinien von GitHub, die Dokumentation zum Citation File Format sowie die verlinkten Beispiele von pandas und TensorFlow zu prüfen, um die erforderlichen Metadaten für mypy zu identifizieren. Die Aufgabe ist erledigt, wenn die Datei vollständige, gültige Zitationsmetadaten enthält und GitHub daraus APA- und BibTeX-Zitate generieren kann.