add release notes

Author: localspook

clang-tools-extra/docs/ReleaseNotes.rst

@@ -257,6 +257,10 @@ Changes in existing checks
   <clang-tidy/checks/modernize/use-designated-initializers>` check to
   suggest using designated initializers for aliased aggregate types.
 
+- Improved :doc:`modernize-use-nullptr
+  <clang-tidy/checks/modernize/use-nullptr>` check by fixing a crash
+  on Windows when the check was enabled with a 32-bit clang-tidy binary.
+
 - Improved :doc:`modernize-use-std-format
   <clang-tidy/checks/modernize/use-std-format>` check to correctly match
   when the format string is converted to a different type by an implicit