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

[Roundup Robot]

Roundup Robot added the comment:

New changeset 52038705827d by Yury Selivanov in branch '3.6':
Issue #28635: Document Python 3.6 opcode changes
https://hg.python.org/cpython/rev/52038705827d

New changeset 48fb6a4cb5f8 by Yury Selivanov in branch 'default':
Merge 3.6 (issue #28635)
https://hg.python.org/cpython/rev/48fb6a4cb5f8

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