[docs] [issue23677] Mention dict and set comps in library reference

[Ezio Melotti]

Changes by Ezio Melotti <ezio.melotti at gmail.com>:


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nosy: +ezio.melotti
stage:  -> patch review
type:  -> enhancement
versions: +Python 3.6 -Python 3.4

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue23677>
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