fix: Skill 加 Setup 引导，纯 Skill 安装也能自动触发 pip install

SKILL.md 增加 Setup 段：Agent 读到 skill 后先检测 agent-reach CLI
是否存在，不存在则自动 pip install + agent-reach install。
README 说明同步更新。

agent-reach/SKILL.md

@@ -14,6 +14,24 @@ description: >
 
 Read and search the internet across 9+ platforms via unified CLI.
 
+## Setup
+
+First check if agent-reach is installed:
+```bash
+agent-reach doctor
+```
+
+If command not found, install it:
+```bash
+pip install https://github.com/Panniantong/agent-reach/archive/main.zip
+agent-reach install --env=auto
+```
+
+`install` auto-detects your environment and installs all dependencies (Node.js, mcporter, bird CLI, gh CLI). Read the output and run `agent-reach doctor` to see what's active.
+
+For channels that need user input, ask the user. See the full setup guide:
+https://raw.githubusercontent.com/Panniantong/agent-reach/main/docs/install.md
+
 ## Commands
 
 ### Read any URL