[docs] [issue28738] Document SIGBREAK as argument for signal() under Windows.

[Eryk Sun]

Changes by Eryk Sun <eryksun+pybugs at gmail.com>:


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keywords: +easy
priority: normal -> low
stage:  -> patch review
versions: +Python 3.6

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue28738>
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