[faiproject/fai] 0fe545: explain in more detail that LOGUSER is defined in ...

[Mrfai]

  Branch: refs/heads/master
  Home:   https://github.com/faiproject/fai
  Commit: 0fe5455f62c073553b6e17f59c8cc80d21befcbc
      https://github.com/faiproject/fai/commit/0fe5455f62c073553b6e17f59c8cc80d21befcbc
  Author: Thomas Lange <lange at debian.org>
  Date:   2022-06-13 (Mon, 13 Jun 2022)

  Changed paths:
    M conf/fai.conf
    M doc/fai-guide.txt
    M examples/simple
    M man/fai.conf.5

  Log Message:
  -----------
  explain in more detail that LOGUSER is defined in two locations