[docs] [issue36329] use the right python "make -C Doc/ serve"

[Stéphane Wirtel]

Change by Stéphane Wirtel <stephane at wirtel.be>:


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keywords: +patch
pull_requests: +12342
stage:  -> patch review

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue36329>
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