fix release note + mention diag message fix

Author: 5chmidti

clang-tools-extra/docs/ReleaseNotes.rst

@@ -133,8 +133,9 @@ Changes in existing checks
   member function calls too.
 
 - Improved :doc:`readability-enum-initial-value
-  <clang-tidy/checks/readability-enum-initial-value>` check to only issue
-  diagnostics for the definition of an ``enum``.
+  <clang-tidy/checks/readability/enum-initial-value>` check by only issuing
+  diagnostics for the definition of an ``enum``, and by fixing a typo in the
+  diagnostic.
 
 - Improved :doc:`performance-avoid-endl
   <clang-tidy/checks/performance/avoid-endl>` check to use ``std::endl`` as