Provide NeRF Eval Instructions

[vorasaurus]

Update documentation to include NeRF eval command i.e. to populate NeRF sigma grids, required for training second phase semantic module (include instructions to install additional required packages, e.g. kubric).

[duckworthd]

Acknowledged. Working on it.

[duckworthd]

Clarification: Provide documentation for

1. Training NeRF models (in parallel)
2. Evaluating the quality of said NeRF models
3. Training NeSF semantic modules (requires pretrained NeRF models)
4. Evaluating NeSF semantic module