It’s poorly organized and not without errors, but there is basic setup and customization doc.
https://github.com/keyboardio/Model01-Firmware/blob/master/README.md (https://github.com/keyboardio/Model01-Firmware/blob/readme-and-env/README.md is an updated version already a WIP)
And indeed, more in Remapping keys? - #23 by algernon