docs: add README

Project overview, tool table, doc index with cross-links.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: AlbinoGeek

README.md

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+# @rethunk/github-mcp
+
+[![CI](https://github.com/Rethunk-AI/rethunk-github-mcp/actions/workflows/ci.yml/badge.svg)](https://github.com/Rethunk-AI/rethunk-github-mcp/actions/workflows/ci.yml)
+[![License: MIT](https://img.shields.io/badge/license-MIT-blue.svg)](LICENSE)
+
+**Rollup GitHub tools over MCP** — high-value composite operations that batch many GitHub API calls into single MCP tool invocations with concise, LLM-optimized output. Not 1:1 API wrappers; each tool replaces 3-6 round-trips.
+
+**Repository:** [github.com/Rethunk-AI/rethunk-github-mcp](https://github.com/Rethunk-AI/rethunk-github-mcp) · **GitHub Packages (CI on each tag):** [`@rethunk-ai/github-mcp`](https://github.com/Rethunk-AI/rethunk-github-mcp/packages) — see [docs/install.md](docs/install.md) and [HUMANS.md](HUMANS.md) Publishing.
+
+## Tools
+
+| Tool | What it does |
+|------|-------------|
+| **`repo_status`** | Multi-repo dashboard: branch HEAD, CI, PRs, issues, latest commit — up to 20 repos in one call |
+| **`my_work`** | Cross-repo personal queue: your open PRs, review requests, assigned issues |
+| **`pr_preflight`** | Pre-merge safety check: mergeable, reviews, CI, behind-base, computed `safe` verdict |
+| **`release_readiness`** | What would ship now: unreleased commits, associated PRs, CI on head, diff stats |
+| **`ci_diagnosis`** | Why is CI red: failed run logs (tail-truncated), trigger commit, run URL |
+| **`org_pulse`** | Org-wide dashboard: failing CI, stale PRs, unreviewed PRs across all active repos |
+
+All tools are **read-only** and support **markdown** (default) or **JSON** output.
+
+## Documentation
+
+| Doc | Audience |
+|-----|----------|
+| **[docs/install.md](docs/install.md)** | Prerequisites, running the package, every supported MCP client, troubleshooting |
+| **[docs/mcp-tools.md](docs/mcp-tools.md)** | Tool ids, parameters, JSON output shapes, error codes (canonical reference) |
+| **[HUMANS.md](HUMANS.md)** | Auth, dev commands, CI, publishing |
+| **[AGENTS.md](AGENTS.md)** | Contributors: implementation map, API strategy, contracts, CI |