just cut and paste the commands there into a vanilla openSUSE Leap 15.2 install as per the Readme.
The associated forum thread that introduced this is here:
You just need an openSUSE Leap 15.2 install, say in a virtual machine, in order to get and use the self contained builder. All in the readme in the above repo.
No hand compiling and the iso is build using those instructions and repo. It’s a kiwi-ng configuration that build the iso from start to finish and includes our official rpms within it.