Copyright for bigint source package in Focal

Format: https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
Upstream-Name: bigint
Upstream-Contact: Matt McCutchen 

Files: *
Copyright: Matt McCutchen 
License: public-domain

Files: debian/*
Copyright: Boyuan Yang 
License: CC0-1.0

License: CC0-1.0
 On Debian systems, the full text of the CC0 1.0 Universal
 License can be found in the file
 "/usr/share/common-licenses/CC0-1.0".

License: public-domain
 I, Matt McCutchen, the sole author of the original Big Integer Library,
 waive my copyright to it, placing it in the public domain.
 The library comes with absolutely no warranty.