Two small changes in using/windows (#159438)

Thes are based on Steve Dower's answer (to my questions) at
https://discuss.python.org/t/python-3-16-0-alpha-1-is-now-available/109466/11.

Update sentence about updates to note that site-packages and Scripts
directories are left alone.

Add a link to the administer configuration section.
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Co-authored-by: Steve Dower <steve.dower@microsoft.com>