Add example usage for formatting a floppy disk.

[murray]

Summary

This media was introduced in the 1980s and providing a more
complete example here will allow us to simplify and modernize the
FreeBSD Handbook.

Test Plan

Review formatted output.

[bcr]

A comment about a sentence fragment. The rest looks good.
Do you know about textproc/igor? You can run it over the man page and it will give you some additional style tips and warnings. It will definitely complain about the .Dd not being set to today. For each content change that is relevant enough (like this one), we bump this to the date when the commit happens (i.e. when you get the approval).
Additionally, you can check the man page with "mandoc -Tlint" to see if there are some tags out of place or something.

usr.sbin/fdformat/fdformat.8

137 ↗

(On Diff #72150)

the "in inserted" seems out of place. Was that part of a different sentence or a rewrite? ;-)

[murray]

Address reviewer feedback about errant word in a sentence, and
clean up some formatting issues found by mandoc -Tlint and igor.

[bcr]

Looks good now, ready to commit (and MFC later)! Thank you.