runtime(doc): Update advice for [gnt]roff users

runtime(doc): Update advice for [gnt]roff users

Content:
* Offer more specific guidance regarding input line breaks and sentence
  endings.
* Advise what to do when a line ends with sentence-ending punctuation
  but doesn't end a sentence.
* Advise against use of blanks lines and leading spaces for formatting
  when a macro package is in use.
* Advise how to achieve visual separation in the document without
  affecting formatting.
* Point out how the newline/end-of-sentence rules aid diffing.
* Distinguish the separate processes of inter-sentence space
  supplementation and filling.
* Use conventional (but accessible) terms from typography instead of
  more casual, approximate ones.
* Clarify what sort of extension the ms package's `XP` macro is.

Style:
* Fix comma splice with a semicolon.
* Use slightly more standard/idiomatic English.

Sources:
* https://rhodesmill.org/brandon/2012/one-sentence-per-line/
* https://www.ualberta.ca/en/computing-science/media-library/docs/unix-beginners.pdf
  (p. 20)
* https://www.gnu.org/software/groff/manual/groff.html.node/Input-Conventions.html
* https://cgit.git.savannah.gnu.org/cgit/groff.git/tree/doc/ms.ms?h=1.23.0#n1131
* https://docs-archive.freebsd.org/44doc/usd/18.msdiffs/paper.pdf

closes: #19193

Signed-off-by: G. Branden Robinson <g.branden.robinson@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>