Add `llms.txt` with `vitepress-plugin-llms`

### Documentation is

- [ ] Missing
- [ ] Outdated
- [ ] Confusing
- [ ] Not sure

### Explain in Detail

Add docs for LLMs

### Your Suggestion for Changes

Add this VitePress plugin - https://github.com/okineadev/vitepress-plugin-llms

### Relevant Page

_No response_

### Reproduction (Optional)

_No response_

### Steps to reproduce (Optional)

_No response_