gh-89253: Add 3.10 whatsnew section for itertools.pairwise (GH-91563)

#89253

[`pairwise()`](https://docs.python.org/3/library/itertools.html#itertools.pairwise) already has the 'new in python3.10'

Automerge-Triggered-By: GH:rhettinger

Author: slateny

Doc/whatsnew/3.10.rst

@@ -1223,6 +1223,12 @@ now call :func:`inspect.get_annotations` to retrieve annotations. This means
 also now un-stringize stringized annotations.
 (Contributed by Larry Hastings in :issue:`43817`.)
 
+itertools
+---------
+
+Add :func:`itertools.pairwise()`.
+(Contributed by Raymond Hettinger in :issue:`38200`.)
+
 linecache
 ---------