Improve support for and documentation of custom models

[Jack-Khuu]

🚀 The feature, motivation and pitch

torchchat supports adding models to the "known_model" list and has CLI support for local models not hosted in torchchat's, but this can be better documented.

Alternatives

No response

Additional context

Some PR's Related to this theme:

• How to deploy a new model by torchchat? #1038
• support load model locally #1040

RFC (Optional)

No response

[Jack-Khuu]

https://github.com/pytorch/torchchat/blob/main/docs/local-model.md

More work to come this half, closing issue