Add missing ReleaseNotes.rst update

Author: foxfromabyss

clang/docs/ReleaseNotes.rst

@@ -297,6 +297,8 @@ Attribute Changes in Clang
 
 Improvements to Clang's diagnostics
 -----------------------------------
+- Diagnostics messages now refer to ``structured binding`` instead of ``decomposition``,
+  since `P0615R0 <https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0615r0.html>`_ changed the term.
 - Added a separate diagnostic group ``-Wfunction-effect-redeclarations``, for the more pedantic
   diagnostics for function effects (``[[clang::nonblocking]]`` and ``[[clang::nonallocating]]``).
   Moved the warning for a missing (though implied) attribute on a redeclaration into this group.