[docs] [issue28089] Document TCP_NODELAY by default

[Ned Deily]

New submission from Ned Deily:

This is marked as a release blocker but, since it's just a doc change, I'm not going to hold 3.6.0 for it.  It would be nice to get it in, though.

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priority: release blocker -> deferred blocker

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue28089>
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