update documentation (#448)

the fedora copr repo is no longer being updated since the maintainer of
it, mamg22, no longer uses nsxiv in his daily setup (and thus stopped
contributing to nsxiv as well).

he has requested the repo and his email to be removed from the project.
so go ahead and honor that request.

also take this as an opportunity to remove some long inactive
maintainers from the CURRENT MAINTAINERS section of the manpage.

Reviewed-on: https://codeberg.org/nsxiv/nsxiv/pulls/448
Reviewed-by: explosion-mental <explosion-mental@noreply.codeberg.org>

README.md

@@ -58,10 +58,6 @@ nsxiv is available on the following distributions/repositories. If you don't see
 your distro listed here, either contact your distro's package maintainer or
 consider packaging it yourself and adding it to the respective community repo.
 
-Repos not tracked by repology:
-
-* Fedora: Enable the copr repo via `dnf copr enable mamg22/nsxiv`.
-
 
 Dependencies
 ------------

etc/nsxiv.1

@@ -569,11 +569,6 @@ TAAPArthur             <taaparthur at gmail.com>
 eylles                 <ed.ylles1997 at gmail.com>
 Stein Gunnar Bakkeby   <bakkeby at gmail.com>
 explosion-mental       <explosion0mental at gmail.com>
-mamg22                 <marcomonizg at gmail.com>
-LuXu
-Guilherme Freire
-Sam Whitehead
-Kian Kasad             <kian at kasad.com>
 .EE
 .SH CONTRIBUTORS
 .EX