Updating incorrect example of PowerShell.Create() - #7926

Updating this documentation, per this issue in Github. MicrosoftDocs/PowerShell-Docs#2938

The overload for powerShell.Create() are either RunSpaceMode, or InitialSessionState. In order to accept a command, one must use the .AddScript method.

PR Summary

Took some digging to find this, but it looks like Docs.Microsoft.Com scrapes files like these to generate the code samples.

The intention is that this change:

• Should happen, as it appears to be incorrect as is today in the comments
• Hopefully will drive an update to this page as well - https://docs.microsoft.com/en-us/dotnet/api/system.management.automation.powershell?view=pscore-6.0.0

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Change is not breaking
• Make sure all .h, .cpp, .cs, .ps1 and .psm1 files have the correct copyright header
• This PR is ready to merge and is not Work in Progress.
  • If the PR is work in progress, please add the prefix WIP: to the beginning of the title and remove the prefix when the PR is ready.
• User-facing changes
  • Not Applicable
  • OR
  • User-facing Documentation needed
    • Issue filed - Issue link:
• Testing - New and feature
  • Not Applicable or can only be tested interactively
  • OR
  • Make sure you've added a new test if existing tests do not effectively test the code changed
    • Add [feature] if the change is significant or affects feature tests