docs: add tool-setup directory with index README

Create docs/tool-setup/ to organize external service configuration
guides in a dedicated subdirectory.

docs/tool-setup/README.md

@@ -0,0 +1,20 @@
+# Tool Setup Guides
+
+Configuration guides for MimiClaw's external service integrations.
+
+## Guides
+
+| Guide | Service | Description |
+|-------|---------|-------------|
+| [Feishu Setup](FEISHU_SETUP.md) | [Feishu / Lark](https://open.feishu.cn/) | Feishu bot channel — receive and send messages via Feishu |
+
+## Overview
+
+MimiClaw integrates with external services to extend its capabilities. Each guide below walks through obtaining API credentials, configuring MimiClaw (build-time or runtime), and verifying the integration.
+
+All credentials can be set in two ways:
+
+1. **Build-time** — define in `main/mimi_secrets.h` and rebuild
+2. **Runtime** — use serial CLI commands (saved to NVS flash, no rebuild needed)
+
+See [mimi_secrets.h.example](../../main/mimi_secrets.h.example) for the full list of configurable secrets.