d/copyright: include full AGPL-3 license text
d/copyright: include full AGPL-3 license text

The AGPL license is not in /usr/share/common-licenses,
so let's include the full text here.

Git-Dch: Ignore
Requested-by: Vincent Cheng <a079987233cbd8d400206ab31b700cb2a66c8e3b@debian.org>
Signed-off-by: Arturo Borrero Gonzalez <6536d6b0723dedf12377d931b2edd2f9488a948b@gmail.com>

aborrero/pkg-liquidprompt