[Gimp-user] Add traditional Linux Builds

[Bill Rich <thebill rich gmail com>]

I understand why flatpak is easier to distribute, but I've had so many
problems using it with other applications, and using plugins, that I
finally uninstalled the flatpak version and went with the package from
https://ubuntuhandbook.org/.
It's great that there are volunteers that make this happen, but I would
rather have the official GIMP installs for Linux include traditional
packages as well as the flatpak. Flatpak works OK enough for dabblers, but
we also want to promote those who do more serious work with it.
Thank you