Suggestion: Add support for flashing other firmwares

[mariomadproductions]

E.g. the ntrboot version of GodMode9

ntrboot_flasher_nds supports this

[kitlith]

This is already possible by replacing ntrboot/boot9strap_ntr.firm and ntrboot/boot9strap_ntr.firm.sha with files based on GodMode9.

If you're asking for anything more, like a menu to select between possible payloads, then it's not likely to happen at this point unless someone submits a PR or there's a big revival in interest in ntrboot and I become interested in adding features again. If you are asking for more, I suggest changing the title of the issue to match.