Cygwin: document the recent pipe changes

winsup/cygwin/release/3.3.0

@@ -23,6 +23,10 @@ What changed:
   rather than a Bnnn constant, as on Linux.
   Addresses: https://cygwin.com/pipermail/cygwin/2021-July/248887.html
 
+- The internal implementation of pipes has been overhauled; this
+  should result in improved performance.
+  Adresses: https://cygwin.com/pipermail/cygwin/2021-August/249238.html
+
 
 Bug Fixes
 ---------

winsup/doc/new-features.xml

@@ -35,6 +35,11 @@ The speed argument to cfsetspeed(3) can now be a numerical baud rate
 rather than a Bnnn constant, as on Linux.
 </para></listitem>
 
+<listitem><para>
+The internal implementation of pipes has been overhauled; this should
+result in improved performance.
+</para></listitem>
+
 </itemizedlist>
 
 </sect2>