The Readme.md instructions said, "Mount the boot partition (of the .img file) to add user-data, meta-data and optionally network-config files to the root of it. Unmount it again, once added."
Are those filenames simply user-data, meta-data and network-config without the suffixes or are they user-data.yaml, meta-data.yaml and optionally network-config.yaml as listed in this project's root and examples directories?