import the debian/copyright file from debian

Co-Authored-By: Angus Lees <gus@inodes.org>
Co-Authored-By: Fabian Grünbichler <f.gruenbichler@proxmox.com>
Co-Authored-By: Hiroaki Nakamura <hnakamur@gmail.com>
Co-Authored-By: Jordan Justen <jljusten@gmail.com>
Co-Authored-By: Luca Bruno <lucab@debian.org>
Co-Authored-By: Sylvestre Ledru <sylvestre@debian.org>
Co-Authored-By: Ximin Luo <infinity0@debian.org>

Author: 8 people