README.txt in the latest build has some of this info.

First thing.

Custom environments. 

If you add an OBJ containing the environment you want, called env.obj, as well as the mtl (if necessary) as env.mtl;

it will load as the environment in the game. Included is an environment from Free3D (author is pabong).

For custom objects,

lace the OBJ in the "Objects" folder and it will appear in the dropdown in the middle of the screen in the Q menu.

Currently there aren't textures, those will (probably) be added in the next build.

Thanks for reading, have a nice day!