Copyright for doc-central source package in Bionic

Copyright 2000 Wichert Akkerman 
Copyright 2004-2005 Guilherme de S. Pastore 

This package is free software; you may redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2, or (at your option) any
later version.

On Debian systems you can find the text of the GNU General Public License
in /usr/share/common-licenses/GPL.