How to create a custom Ubuntu image (deb/3.1/CLI)

by the grace of the universe, I found this post which explains the fix:
https://discourse.maas.io/t/maas-boot-resources-create-fails-with-no-such-file-or-directory/3627/3

there are at least 2 or 3 places in the docs that do NOT mention this key point, can someone please update the docs or give me the perms and I sure will.