docs(readme): 补 Windows 完整步骤一行

[bigbrother666sh]

补一行 Windows 小白向的完整步骤说明：先装 Git Bash（勾 Add to PATH 让 bash 进 PowerShell PATH）→ 再跑 irm | iex。

这行内容此前只存在于 fork (bigbrother666sh/wiseflow) master 的一个本地 commit 里，没走 PR 进 upstream。本轮清理分支时发现，补进来免得丢。

Auto Release 已禁用，合此 PR 不 bump 版本，保持 v5.6.0。README 走 raw URL 拉取，无需重建 tarball。

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