Update get-started.md

[MrEddX]

Fix: Windows - Activation of Virtual Environment Command

[alexvoss]

The command works for me under both Powershell and cmd.exe, while the .bat version does not work under Powershell.

The script runs but fails to modify the environment, no changes to PATH, not changed prompt to indicate I am in a virtual environment. I am speculating a bit here but I think Powershell launches a cmd.exe to run a .bat script? The changes to the environment would be made there and then it exits.

If you have any information about conditions under which the activation of the venv does not work please open an issue. I am closing the PR because appending .bat is not a solution.