DOC: add whatsnew entry

Author: tacaswell

doc/source/whatsnew/v0.21.0.txt

@@ -126,6 +126,7 @@ Other Enhancements
 - :func:`date_range` now accepts 'Y' in addition to 'A' as an alias for end of year (:issue:`9313`)
 - Integration with `Apache Parquet <https://parquet.apache.org/>`__, including a new top-level :func:`read_parquet` and :func:`DataFrame.to_parquet` method, see :ref:`here <io.parquet>`.
 - :func:`DataFrame.add_prefix` and :func:`DataFrame.add_suffix` now accept strings containing the '%' character. (:issue:`17151`)
+- :func:`DataFrame.items` is present in both Python 2 and 3 and is lazy in all cases (:issue:`13918`, :issue:`17213`)
 
 .. _whatsnew_0210.api_breaking: