Add llms.txt for LLM/agent-readable project summary

[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 get a quick, accurate picture of a project instead of crawling and guessing through the full README and 100+ parser doc pages.

Given jc's core use case (piping command output into scripts/automation), it seemed like a natural fit for agent-assisted workflows — an agent asked "how do I parse ifconfig output as JSON" can load this file and go straight to the right parser reference instead of parsing the whole README.

Content is derived entirely from your existing README sections (Installation, Usage, full parser list, Compatibility, Contributing) — no new claims, just pointers into docs that already exist. Validated against the llms.txt spec with llms-txt-lint (disclosure: a small validator tool I maintain — happy to drop that line from the PR if you'd rather not have it).

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