[InterNetNews/inn] 031bc7: Improve readers.conf sample and documentation

[Julien ÉLIE]

  Branch: refs/heads/main
  Home:   https://github.com/InterNetNews/inn
  Commit: 031bc7180d96d94b3c5f9b9324629330688f1256
      https://github.com/InterNetNews/inn/commit/031bc7180d96d94b3c5f9b9324629330688f1256
  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.