[docs] [issue30935] document the new behavior of get_event_loop() in Python 3.6

[miss-islington]

Change by miss-islington <mariatta.wijaya+miss-islington at gmail.com>:


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keywords: +patch
pull_requests: +6845

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue30935>
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