Link Tachyon from release highlights

Author: hugovk

Doc/whatsnew/3.15.rst

@@ -67,6 +67,8 @@ Summary -- Release highlights
 
 * :pep:`799`: :ref:`A dedicated profiling package for organizing Python
   profiling tools <whatsnew315-profiling-package>`
+* :pep:`799`: :ref:`Tachyon: High frequency statistical sampling profiler
+  profiling tools <whatsnew315-sampling-profiler>`
 * :pep:`686`: :ref:`Python now uses UTF-8 as the default encoding
   <whatsnew315-utf8-default>`
 * :pep:`782`: :ref:`A new PyBytesWriter C API to create a Python bytes object