docs(readme): add table of contents

The README crossed 200 lines with eight H2 sections and no navigation
aid, forcing readers to scroll to find whether it solves their
problem before they've decided anything. AAA+ B-axis order 32, round 2.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XZzcSbaiw9nR686HDrF8KN

README.md

@@ -16,6 +16,18 @@ unicode-carrier smuggling or active content in untrusted text, on any runtime.
 
 **It holds no runnable code.** Data, specifications and fixtures only.
 
+## Table of Contents
+
+- [Install](#install)
+- [Requirements](#requirements)
+- [What it does](#what-it-does)
+- [Non-goals](#non-goals)
+- [Known limitations](#known-limitations)
+- [Contributing](#contributing)
+- [Reporting a wrong entry](#reporting-a-wrong-entry)
+- [Changelog](#changelog)
+- [License](#license)
+
 ## Install
 
 Nothing to install — this repository is **vendored into consumers**, not installed.