[docs] [issue28635] Update What's New for 3.6

[Roundup Robot]

Roundup Robot added the comment:

New changeset cb4ad88fdc91 by Yury Selivanov in branch '3.6':
Issue #28635: Drop the note that whatsnew is incomplete
https://hg.python.org/cpython/rev/cb4ad88fdc91

New changeset c4d6ef15bb7c by Yury Selivanov in branch '3.6':
Issue #28635: asyncio-related fixes and additions.
https://hg.python.org/cpython/rev/c4d6ef15bb7c

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