clarify licensing

debian/copyright

@@ -0,0 +1,23 @@
+Format: https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
+Source: https://github.com/lretq/fake-battery
+Upstream-Name: fake-battery
+
+Files:
+ *
+Copyright: 2026 Vincent Schweiger <vincent.schweiger@icloud.com>
+License: GPL-2
+ 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 2 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, see &lt;https://www.gnu.org/licenses/&gt;.
+Comment:
+ On Debian systems, the full text of the GNU General Public License
+ version 2 can be found in the file '/usr/share/common-licenses/GPL-2'.