bpo-34317:Improve docstring windows.rst Environment variables in Windows NT

[ghost]

Expired link in windows.rst:
https://support.microsoft.com/en-us/help/100843/environment-variables-in-windows-nt

May I make a suggestion?

The new link:https://www.microsoft.com/en-us/wdsi/help/folder-variables

https://bugs.python.org/issue34317

[the-knights-who-say-ni]

Hello, and thanks for your contribution!

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[ghost]

I seem to be blocked on "CLA not signed". The CPython devguide says:
I've signed and submitted the CLA.

{"HiyashiChuka":true}
https://bugs.python.org/user?@template=clacheck&github_names=HiyashiChuka

Please let me know if there's anything that needs correcting.

[miss-islington]

Thanks @HiyashiChuka for the PR, and @Mariatta for merging it 🌮🎉.. I'm working now to backport this PR to: 3.6, 3.7.
🐍🍒⛏🤖

[bedevere-bot]

GH-8640 is a backport of this pull request to the 3.7 branch.

[miss-islington]

Sorry, @HiyashiChuka and @Mariatta, I could not cleanly backport this to 3.6 due to a conflict.
Please backport using cherry_picker on command line.
cherry_picker 46ebe61c7f3511b97268b44d5373a9e9cf0b5cc7 3.6

[Mariatta]

Thanks @HiyashiChuka and congrats on your first contribution to CPython 🌮