README instructions and build-disk action refer to disk_config/iso.toml which is non-existent.

• disk_config contains iso-gnome.toml and iso-kde.toml

To work around you can:

• copy iso-gnome.toml or iso-kde.toml to iso.toml and modify contents as instructed by README.
• modify iso-gnome.toml or iso-kde.toml as instructed for iso.toml in README and modify build-disk.yml to use desired file.