Hi, glad to hear you're intrested in Thermite
Unfortunatly you are right that there isn't much documentation available at the moment. The reason is that until recently it has really just been a tech demo, without any way to actually write a game based on it. This has changed over the last couple of months with the addition of scripting support but we haven't yet made an official release with such support enabled. We expect to do so within the next couple of months.
In the meantime you can pull the latest version from SVN and browse the code, provided you don't mind that it is stil a little messy. Some things to look out for:
1) The main scriptable classes are in 'Thermite\trunk\Thermite\include\scriptable'. These are the classes which user scripts will be able to interact with. They are all quite simple except the volume class (which has to handle the regeneration of the PolyVox meshes).
2) Example scripts are available 'TechDemo\scripts' which show the creation of lights, entities, etc.
3) The various objects are rendered with Ogre, and 'ThermiteGameLogic::update()' takes care of syncronising the the Ogre representations with Thermite's own versions.
4) Any knowledge of Ogre will be useful - for example models in the game will be in Ogre's .mesh format and Ogre's material scripts are used to control the appearence of the voxel surface in the engine.
Ask if you have any questions, and everything will be a lot easier in a couple of months when we make the next official release...