Wrong command to activate virtual environment in Windows

[zhangjiale-64]

Describe the issue:
According to the readme , an error occurred when running the following command, the Windows environment does not support running this command.

Environment:

• azd version 1.9.5 (commit cd2b7af9995d358aab33c782614f801ac1997dde)
• OS: Windows

Suggestions:
Add command to activate the virtual environment on Windows.

Expected Behavior:
Successfully activated the virtual environment on windows.

@jongio and @marlenezw for notification.