manualpages: Complete the list of user manual pages

manualpages: Complete the list of user manual pages

Jon Murphy gathered all the links and made the updated file
available on the mailing list:
https://lists.ipfire.org/pipermail/development/2021-October/011383.html
https://lists.ipfire.org/pipermail/development/2021-December/011737.html

With kind permission from him, this patch contains the completed list.
The list was successfully checked with "./make.sh check-manualpages".

Signed-off-by: Leo-Andres Hofmann <hofmann@leo-andres.de>
Reported-by: Jon Murphy <jcmurphy26@gmail.com>
Reviewed-by: Peter Müller <peter.mueller@ipfire.org>