Merge branch 'debian-copyright-file' into 'master'

debian: Add copyright file

See merge request !1

debian/copyright

+Format: https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
+Upstream-Name: Calls
+Source: https://source.puri.sm/Librem5/calls
+License: GPL-3+
+
+Files: *
+Copyright: 2018 Purism SPC
+License: GPL-3+
+ This program is free software; you can redistribute it and/or modify it under
+ the terms of the GNU General Public License as published by the Free Software
+ Foundation; either version 3 of the License, or (at your option) any later
+ version.
+ .
+ This program is distributed in the hope that it will be useful, but WITHOUT
+ ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
+ details.
+ .
+ You should have received a copy of the GNU General Public License along with
+ this package; if not, write to the Free Software Foundation, Inc., 51 Franklin
+ St, Fifth Floor, Boston, MA  02110-1301 USA
+ .
+ On Debian systems, the full text of the GNU General Public License version 3
+ can be found in the file `/usr/share/common-licenses/GPL-3'.