[Book] Add reference to models repo

[laggui]

We're starting to have more and more models available for our users so it would be nice to add a small paragraph in the book with a link to the models repo.

[polarathene]

Probably worth a mention on the website too for those who land there?

I noticed the benchmarks (in this repo, and the separate benchmarks repo) lack any contributed results. It'd be nice if someone could provide one for users to get an impression upfront?

---

I had landed at huggingface/candle before burn and liked how their README had a section with direct links to examples, followed by models. It could be a good page in itself early on in the burn book? (unless it's a better fit on the README for discovery)

[laggui]

Good idea! We should probably add the models to the README as well, following the examples (which should probably be better enumerated).