RECIPE FORMAT:
{CORENAME} {COREDIR} {URL} {BRANCH} {ENABLED} {COMMAND} {MAKEFILE} {SUBDIR} {ARGS}

Ex:
2048 libretro-2048 https://github.com/libretro/libretro-2048.git master YES GENERIC Makefile.libretro .

Command should usually be GENERIC and REPOTYPE should usually be project. Notable exceptions are PPSSPP and PICODRIVE. Those are submodule repos.