Update release note for escape sequences

Author: AaronBallman

clang/docs/ReleaseNotes.rst

@@ -123,7 +123,10 @@ C2y Feature Support
 - Implemented `WG14 N3353 <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3353.htm>_`
   which adds the new ``0o`` and ``0O`` ocal literal prefixes and deprecates
   octal literals other than ``0`` which do not start with the new prefix. This
-  feature is exposed in earlier language modes and in C++ as an extension.
+  feature is exposed in earlier language modes and in C++ as an extension. The
+  paper also introduced octal and hexadecimal delimited escape sequences (e.g.,
+  ``"\x{12}\o{12}"``) which are also supported as an extension in older C
+  language modes.
 
 C23 Feature Support
 ^^^^^^^^^^^^^^^^^^^