Add unambiguous GPL header to README
User story: I am a developer wanting to quickly and accurately ascertain the license of the application, so that I know how I can distribute it.
At the moment it is not clear without inspection whether this project is GPLv3-only or GPLv3-or-later. Doing a search for "at your option" reveals that several files have an "or later" header ( https://dev.gajim.org/search?project_id=30&search=at+your+option ) -- which suggests that the intention is for all the code to be GPLv3-or-later?
Options include:
- Adding a GPL header as a paragraph in the README
- Adding a SPDX identifier in the README:
SPDX-License-Identifier: GPL-3.0+
(As a side note, it would be helpful if README and README.html were combined, or one of them renamed so there is only one README.)