web: install.md — move the 'add pmm.exe to PATH' note out of the code block

It was inside the PowerShell code fence, so the Chinese line (with a backslash in
pmm\pmm.exe) rendered as code text. Move it outside as a quoted note (

web/docs/md/install.md

@@ -16,9 +16,10 @@ curl -sSL https://pmm.parlz.com/download/install.sh | bash
 # PowerShell
 Invoke-WebRequest https://pmm.parlz.com/download/pmm-0.3.6-windows-amd64.zip -OutFile pmm.zip
 Expand-Archive pmm.zip -DestinationPath pmm
-# 然后将 pmm\pmm.exe 所在目录加入 PATH
 ```
 
+> 然后将 `pmm\pmm.exe` 所在目录加入 PATH。
+
 ## Debian / Ubuntu（.deb）
 
 ```bash