DOC: 0.22.0 release docs (#18983)

[ci skip]

(cherry picked from commit 4ed58d9)

Author: TomAugspurger

doc/source/release.rst

@@ -37,6 +37,27 @@ analysis / manipulation tool available in any language.
 * Binary installers on PyPI: http://pypi.python.org/pypi/pandas
 * Documentation: http://pandas.pydata.org
 
+pandas 0.22.0
+-------------
+
+**Release date:** December 29, 2017
+
+This is a major release from 0.21.1 and includes a single, API-breaking change.
+We recommend that all users upgrade to this version after carefully reading the
+release note.
+
+The only changes are:
+
+- The sum of an empty or all-*NA* ``Series`` is now ``0``
+- The product of an empty or all-*NA* ``Series`` is now ``1``
+- We've added a ``min_count`` parameter to ``.sum()`` and ``.prod()`` controlling
+  the minimum number of valid values for the result to be valid. If fewer than
+  ``min_count`` non-*NA* values are present, the result is *NA*. The default is
+  ``0``. To return ``NaN``, the 0.21 behavior, use ``min_count=1``.
+
+See the :ref:`v0.22.0 Whatsnew <whatsnew_0220>` overview for further explanation
+of all the places in the library this affects.
+
 pandas 0.21.1
 -------------
 

doc/source/whatsnew/v0.22.0.txt

@@ -1,7 +1,7 @@
 .. _whatsnew_0220:
 
-v0.22.0
--------
+v0.22.0 (December 29, 2017)
+---------------------------
 
 This is a major release from 0.21.1 and includes a single, API-breaking change.
 We recommend that all users upgrade to this version after carefully reading the