NOTE: You have to install luma first in order to configure it. One way to do that is "NTRBoot": https://www.youtube.com/playlist?list=PL1-LwCZ3SdPrB-fPSKbeA3aA0I0NYIIsz (a compatible DS flashcart is required). Sorry for my accent :)
This video shows the remaining steps to kickstart with the custom firmware.