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

Changes by Martin Panter <vadmium+py@gmail.com>: ---------- assignee: docs@python -> martin.panter nosy: +berker.peksag stage: patch review -> commit review _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue16701> _______________________________________