[docs] [issue16701] Docs missing the behavior of += (in-place add) for lists.

[Martin Panter]

Changes by Martin Panter <vadmium+py at gmail.com>:


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assignee: docs at python -> martin.panter
nosy: +berker.peksag
stage: patch review -> commit review

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue16701>
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