man: tweak --sub-codepage for concision

The many "boxes" in this entry were causing rst2pdf to fail because it
couldn't figure out where to break the page. Make the boxes smaller by
removing semi-redundant examples. Also try and make surrounding text a
little shorter by rewording.
Merge pull request #774 from kevmitch/man_pdf_tweaks

man: tweak --sub-codepage for concision