[InterNetNews/inn] 7300d9: Improve readers.conf sample and documentation

[Julien ÉLIE]

  Branch: refs/heads/2.6
  Home:   https://github.com/InterNetNews/inn
  Commit: 7300d9fa2352ffa6d830ffda113540d157abede2
      https://github.com/InterNetNews/inn/commit/7300d9fa2352ffa6d830ffda113540d157abede2
  Author: Julien ÉLIE <Julien-Elie at users.noreply.github.com>
  Date:   2022-02-05 (Sat, 05 Feb 2022)

  Changed paths:
    M doc/pod/readers.conf.pod
    M samples/readers.conf

  Log Message:
  -----------
  Improve readers.conf sample and documentation

Add a sample of auth block using "ckpasswd -f <file>" (a very
common usage).  Also mention in the readers.conf sample file
"ckpasswd" without argument for PAM authentication.

Highlight the fact that auth groups are processed bottom up.

Remove obsolete wording for INN 2.3 and earlier.