docs: add OpenClaw exec permission prerequisite to README (#117)

Fixes #110 and #115. Since OpenClaw 2026-01 disabled the exec tool by
default, users on OpenClaw can't run any agent-reach commands unless
exec is explicitly enabled.

Added:
- Warning callout before '快速上手' explaining exec requirement for
  OpenClaw users with the exact config command to use
- Note in the FAQ 'Compatible with Claude Code / OpenClaw...' entry
  with the same fix instructions

Closes #110
Closes #115

Co-authored-by: neo-minion1 <bot@openclaw.ai>

README.md

@@ -92,6 +92,16 @@ AI Agent 已经能帮你写代码、改文档、管项目——但你让它去
 
 ## 快速上手
 
+> ⚠️ **OpenClaw 用户请先确认 exec 权限已开启**
+>
+> Agent Reach 依赖 Agent 执行 shell 命令（`pip install`、`mcporter`、`xreach` 等）。OpenClaw 从 2026 年 1 月起默认禁用 exec 工具，**安装前请先在 OpenClaw 配置中开启 exec 权限**：
+>
+> ```
+> /config set exec.allow true
+> ```
+> 或在 `~/.openclaw/config.json` 中设置 `"exec": { "allow": true }`。
+> 开启后重新对话即可继续安装。其他平台（Claude Code、Cursor、Windsurf 等）不受此限制。
+
 复制这句话给你的 AI Agent（Claude Code、OpenClaw、Cursor 等）：
 
 ```
@@ -310,6 +320,8 @@ Reddit 封锁数据中心 IP。配置一个住宅代理即可解决：`agent-rea
 <summary><strong>Compatible with Claude Code / Cursor / OpenClaw / Windsurf?</strong></summary>
 
 Yes! Agent Reach is an installer + configuration tool — any AI coding agent that can run shell commands can use it. Works with Claude Code, Cursor, OpenClaw, Windsurf, Codex, and more. Just `pip install agent-reach`, run `agent-reach install`, and the agent can start using the upstream tools immediately.
+
+**OpenClaw note:** Since January 2026, OpenClaw disables the `exec` tool by default. Agent Reach requires exec to run shell commands. Enable it first: `/config set exec.allow true` (or set `"exec": { "allow": true }` in `~/.openclaw/config.json`), then restart the conversation before installing.
 </details>
 
 <details>