Update Question 5.20:

• Generalize text
• Mark up FreeBSD-questions with &a.questions;
• Mark up Peter Wemm with &a.peter;
• Add <replaceable> for minor versions
• Capitalize "ID"s
• Update from sio.c to sio_isa.c
• Mark up sio with <devicename> instead of <literal>

Reviewed by: trhodes, danger, remko
Approved by: gabor (mentor)