[faiproject/fai] 416094: add info about pkgs/ and live ISO

[Mrfai]

  Branch: refs/heads/master
  Home:   https://github.com/faiproject/fai
  Commit: 41609468d2c1ef759c2c027ac21240c8967db38b
      https://github.com/faiproject/fai/commit/41609468d2c1ef759c2c027ac21240c8967db38b
  Author: Thomas Lange <lange at debian.org>
  Date:   2023-12-11 (Mon, 11 Dec 2023)

  Changed paths:
    M doc/fai-guide.txt

  Log Message:
  -----------
  add info about pkgs/ and live ISO