Copyright for stress-ng source package in Nile V2.0

Format: https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
Upstream-Name: stress-ng
Upstream-Contact: Colin King 
Source: git://kernel.ubuntu.com/cking/stress-ng.git

Files: *
Copyright: 2013-2020, Canonical, Ltd.
License: GPL-2+
 On Debian systems, the complete text of the GNU General Public
 License can be found in `/usr/share/common-licenses/GPL-2'.