Update installation.md (laravel#10023)

* Update installation.md

The proposed PowerShell command does not work if the PowerShell is not run as Administrator. If that's the case, the PowerShell just disappears without any error on both Windows 10 and Windows 11. By running the PowerShell as an administrator, the command is executed with success.

* Update installation.md

---------

Co-authored-by: Taylor Otwell <[email protected]>

Author: sfolador

installation.md

@@ -70,6 +70,7 @@ If you don't have PHP and Composer installed on your local machine, the followin
 ```
 
 ```shell tab=Windows PowerShell
+# Run as administrator...
 Set-ExecutionPolicy Bypass -Scope Process -Force; [System.Net.ServicePointManager]::SecurityProtocol = [System.Net.ServicePointManager]::SecurityProtocol -bor 3072; iex ((New-Object System.Net.WebClient).DownloadString('https://php.new/install/windows'))
 ```