Add llms.txt

[Idered]

Spec: https://llmstxt.org/

Large language models increasingly rely on website information, but face a critical limitation: context windows are too small to handle most websites in their entirety. Converting complex HTML pages with navigation, ads, and JavaScript into LLM-friendly plain text is both difficult and imprecise.

While websites serve both human readers and LLMs, the latter benefit from more concise, expert-level information gathered in a single, accessible location. This is particularly important for use cases like development environments, where LLMs need quick access to programming documentation and APIs.

[ZerdoX-x]

https://svelte.dev/docs/llms

go LocalLLaMA!

[brc-dd]

Was fixed by #3202