PowerShell - feedback for README

[Vivihung]

Here are my feedback for README.md:

1. Step 2: Add instructions in notepad $profile step - notepad will prompt you to create a profile if not finding one.
2. Step 3: Add hyperlink to powershell_plugin.ps1
3. Step 4: Replace python script with codex_query.py
4. Step 5: I don't think the execution policy should be set to the current user. It's not secure in general. Can we use Process instead of CurrentUser? If we do need CurrentUser, then please consider adding instructions to remove the Policy afterward - refer to https://docs.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_execution_policies?view=powershell-7.2#remove-the-execution-policy
   
5. We should list having Python registered in PATH as a prerequisite for PowerShell users.