We don't use the "pseudo-device" configuration option any longer,

We don't use the "pseudo-device" configuration option any longer,
so update the example to use the correct definition.

Add an example for documenting kernel compile options, along with
a small example of how to reference them in the main text of the
man page (I.e. the .Dv macro).

Inspired-by:  a brief exchange I saw in in the commit messages mail