bpo-39417: Fix broken link to guide to building venvs

[j9ac9k]

Fix broken link in python packaging user guide

[bpo-39417](https://bugs.python.org/issue39417): Fix broken link to "See also: Python Packaging User Guide: Creating and using virtual environments"

https://bugs.python.org/issue39417

[the-knights-who-say-ni]

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[j9ac9k]

I have signed the CLA and am waiting the 1 US Business Day before checking the status on the check-python-cla website

[ammaraskar]

Thanks for your contribution @j9ac9k! Could you put the bugs.python.org issue number in the commit message and PR title as shown here: https://devguide.python.org/pullrequest/#making-good-commits

[j9ac9k]

sorry for the multiple forced commits, I got a bit configured in the docs with what the format should be of the git commit msg; git commit msg should now be correct.

[ammaraskar]

LGTM once CLA is approved.

[bonitobird]

At PyCascades Sprint, this is good to go. @willingc Please review.

[miss-islington]

Thanks @j9ac9k for the PR, and @willingc for merging it 🌮🎉.. I'm working now to backport this PR to: 3.8.
🐍🍒⛏🤖

[bedevere-bot]

GH-21383 is a backport of this pull request to the 3.8 branch.