[MODDING] Add model documentation

[JeodC]

There is currently no documentation for model modding. Fast64 plugin for Blender needs to support BK64, ideally. The Hackpack community has ample documentation for model mods in romhacking, which may shed some light.

[JeodC]

HarbourMasters/fast64#69

Fast64 support added. When merged and solidified, update the documentation in Lighthouse.