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

Changes by Ezio Melotti <ezio.melotti@gmail.com>: ---------- nosy: +ezio.melotti stage: -> patch review type: -> enhancement versions: +Python 3.6 -Python 3.4 _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue23677> _______________________________________