Docs/CLI Primer: Add PowerShell tip

This tip came up in the Zulip chat when I was having issues building my site on Windows.

Update the CLI Primer page with this info:

If you got the "running scripts is disabled" message while using Antora in Powershell, you can get around that with this command while running PowerShell as an administrator:

Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope LocalMachine

Other option is to just use the Command Prompt.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information