adjkerntz.8: minor cleanup (markup, spdx, reflow)

+ real-time and rtc added to search keywords

• local dropped from search keywords

+ ntpd added to see also
+ use machine independent language

Reported by: emaste (MI language)
MFC after: 3 days
Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/1326