REUSE compliance for all 3 repositories

[AFCMS]

https://reuse.software

https://spdx.github.io/spdx-spec

Nice to have, not a priority at all

[AFCMS]

Limitation is that license files are supposed to be inside a LICENSES folder, that GitHub doesn't search for licenses meaning the GitHub license preview doesn't work.

Each file license and copyright are specified but only the GPLv3 text is present at the root of the repository.

I prefer a nice GitHub preview than a full 100% REUSE compliance and I don't want to duplicate the files.

Anyways these are the issues to licensee:

• Scan folder and all sub-folders for licenses licensee/licensee#603
• Scan LICENSES folder (and maybe other common folders) licensee/licensee#737