top.1: Begin documenting modes in DISPLAY

[ziaee]

Summary

This is obviously not ready, but here's a draft with what i could figure
out so far. The commit log is suprisingly unhelpful, but I found ivct on
a mail from two decades ago and figured I'd get started and throw up a
draft for discussion.

There's some duplication here but I can't think of a more logical way to
do it initially.

[bcr]

usr.bin/top/top.1

391

Capitalize CPU

400

This "If" needs to be on a line of its own after a sentence stop.

445

Capitalize CPU here and in other instances below, too?

460

s/io/IO/

[ziaee]

The problem is that these modes are a literal lowercase option. I think that makes them command modifiers? In which case they should actually be .Cm cpu and .Cm io.