doc: Clarify the errhint example
The errhint example wasn't using the mandated style for errhint
which was needlessly confusing. Fix by rewriting it using the
mandated style.
Reported-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Gurjeet Singh <gurjeet@singh.im>
Reviewed-by: Jonathan S. Katz <jkatz@postgresql.org>
Discussion: https://postgr.es/m/
F02F4B4F-7B7E-406A-B25A-
FF2AA300AB9A@yesql.se