Add release note

Author: antangelo

clang/docs/ReleaseNotes.rst

@@ -513,6 +513,11 @@ Bug Fixes to C++ Support
   rather than prefer the non-templated constructor as specified in
   [standard.group]p3.
 
+- Fix a bug where implicit deduction guides are not correctly generated for nested template
+  classes. Fixes:
+  (`#46200 <https://github.com/llvm/llvm-project/issues/46200>`_)
+  (`#57812 <https://github.com/llvm/llvm-project/issues/57812>`_)
+
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 - Fixed an import failure of recursive friend class template.