Add license file and the image badge for this repository.

The cc-by-sa-3.0 lilcense is the best to be used on Wikipedia.
https://en.wikipedia.org/wiki/Wikipedia:Uploading_images#Copyrighted_images_with_no_license

CC BY-SA 3.0 is simplest, because Wikipedia's text already uses that license

Maybe GitHub recognize cc-by-sa license according to the following page.

https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/licensing-a-repository

Creative Commons Attribution Share Alike 4.0 | cc-by-sa-4.0

The license file is https://creativecommons.org/choose/non-web-popup?license_code=by-sa&jurisdiction=&version=3.0&lang=en .

The image badge is https://creativecommons.org/choose/results-one?license_code=by-sa&jurisdiction=&version=3.0&lang=en .