[docs] [issue35821] Clarify when logging events are propagated when propagate is true

[Karthikeyan Singaravelan]

Change by Karthikeyan Singaravelan <tir.karthi at gmail.com>:


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nosy: +vinay.sajip, xtreak

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35821>
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