Add PowerShell instructions in Windows How To

[Jonathan Biemond]

Currently the How To for installing Django on Windows includes an instruction to activate the virtual environment with the batch script.

...\> project-name\Scripts\activate.bat

​https://docs.djangoproject.com/en/6.1/howto/windows/#setting-up-a-virtual-environment

Many Windows users are likely to be using PowerShell, and instead they need to use:

...\> project-name\Scripts\activate.ps1

Let's update the tutorial to include the instructions for PowerShell.

[Jonathan Biemond]

It's worth noting that the next error PowerShell users are likely to run into is being blocked by the ​Execution Policy.

I think this is worth a separate ticket (pending this one's acceptance). Some prior discussion on the forum: ​https://forum.djangoproject.com/t/virtual-environment-on-windows/8445