Add llms.txt

[abyworkings-coder]

This repo doesn't have an llms.txt file yet — a small, curated markdown index (title, one-line summary, and grouped links to the docs that matter) that AI coding agents can read to understand a project quickly, instead of having to crawl and guess.

yq's detailed docs live on gitbook, separate from the repo. This llms.txt pulls the key usage patterns and doc links that already exist in the README's Quick Usage Guide and Features list into a repo-local index, so an agent working from the repo alone (no network access to the gitbook site, or just working faster from local files) has something self-describing to start from.

Content is derived entirely from your existing README — no new claims, just pointers, organized per the llms.txt spec's Usage / Install / Optional convention. Validated against the llms.txt spec with llms-txt-lint (disclosure: a small validator tool I maintain).

Totally understand if this isn't something you want to maintain — no worries either way, feel free to close.