Update to 2.0

Changelog:
https://gitlab.com/alfix/sysctlview/-/blob/master/CHANGELOG

• Update COMMENT, pkg-descr, and DESKTOP_ENTRIES.

Also, while here:

• Pet portclippy & portfmt.
• Simplify do-install.
• Update installation path for manpages.

PR: 244367
Submitted by: Alfonso S. Siciliano <alfix86@gmail.com>
Approved by: Alfonso S. Siciliano (maintainer)