Add a What's New entry.

Author: serhiy-storchaka

Doc/whatsnew/3.10.rst

@@ -70,6 +70,10 @@ Summary -- Release highlights
 New Features
 ============
 
+* Asynchronous comprehensions are now allowed inside comprehensions in
+  asynchronous functions. Outer comprehensions implicitly become
+  asynchronous. (Contributed by Serhiy Storchaka in :issue:`33346`.)
+
 * The :class:`int` type has a new method :meth:`int.bit_count`, returning the
   number of ones in the binary expansion of a given integer, also known
   as the population count. (Contributed by Niklas Fiekas in :issue:`29882`.)