Add release notes

Author: frederick-vs-ja

libcxx/docs/ReleaseNotes/21.rst

@@ -42,6 +42,7 @@ Implemented Papers
 - P0767R1: Deprecate POD (`Github <https://github.com/llvm/llvm-project/issues/104013>`__)
 - P1361R2: Integration of chrono with text formatting (`Github <https://github.com/llvm/llvm-project/issues/100014>`__)
 - P2255R2: A type trait to detect reference binding to temporary (implemented the type traits only) (`Github <https://github.com/llvm/llvm-project/issues/105180>`__)
+- P2322R6: ``ranges::fold`` (implemented ``ranges::fold_left_first`` and ``ranges::fold_left_first_with_iter``) (`Github <https://github.com/llvm/llvm-project/issues/105208>`__)
 
 Improvements and New Features
 -----------------------------

libcxx/docs/Status/Cxx23Papers.csv

@@ -65,7 +65,7 @@
 "`P2286R8 <https://wg21.link/P2286R8>`__","Formatting Ranges","2022-07 (Virtual)","|Complete|","16",""
 "`P2291R3 <https://wg21.link/P2291R3>`__","Add Constexpr Modifiers to Functions ``to_chars`` and ``from_chars`` for Integral Types in ``<charconv>`` Header","2022-07 (Virtual)","|Complete|","16",""
 "`P2302R4 <https://wg21.link/P2302R4>`__","``std::ranges::contains``","2022-07 (Virtual)","|Complete|","19",""
-"`P2322R6 <https://wg21.link/P2322R6>`__","``ranges::fold``","2022-07 (Virtual)","","",""
+"`P2322R6 <https://wg21.link/P2322R6>`__","``ranges::fold``","2022-07 (Virtual)","|Partial|","","Only ``in_value_result``, ``fold_left_with_iter``, ``fold_left``, ``fold_left_first_with_iter``, and ``fold_left_first`` are implemented."
 "`P2374R4 <https://wg21.link/P2374R4>`__","``views::cartesian_product``","2022-07 (Virtual)","","",""
 "`P2404R3 <https://wg21.link/P2404R3>`__","Move-only types for ``equality_comparable_with``, ``totally_ordered_with``, and ``three_way_comparable_with``","2022-07 (Virtual)","","",""
 "`P2408R5 <https://wg21.link/P2408R5>`__","Ranges iterators as inputs to non-Ranges algorithms","2022-07 (Virtual)","","",""