Update powershell example

*Issue*

Windows now mostly uses Powershell V2, not `powershell.exe`

*Ask*

Consider updating https://github.com/casey/just/blob/master/examples/powershell.just

set windows-shell := ["pwsh.exe", "-NoLogo", "-Command"]

Open examples/powershell.just and compare its current shell example with the command shown in the issue. Update the example to reflect the requested PowerShell executable and options, then verify that the file remains valid and clearly demonstrates the intended Windows shell configuration.

Written by the indexing model from the issue text.