Update docs for 2.2.0RC3

Change-Id: I56a7ac2fdc33293c5abb3685de21811caa37997c

CITATION.cff

diff --git a/CITATION.cff b/CITATION.cff
index 145252c..c8dfa36 100644
--- a/CITATION.cff
+++ b/CITATION.cff
@@ -9,7 +9,7 @@
   given-names: Keir
 - name: The Ceres Solver Team
 version: 2.2
-date-released: 2023-10-02
+date-released: 2023-10-09
 license: Apache-2.0
 repository-code: https://github.com/ceres-solver/ceres-solver
 url: http://ceres-solver.org

docs/source/version_history.rst

diff --git a/docs/source/version_history.rst b/docs/source/version_history.rst
index 2eaa26e..c3e1e8d 100644
--- a/docs/source/version_history.rst
+++ b/docs/source/version_history.rst
@@ -50,6 +50,8 @@
 
 Bug Fixes & Minor Changes
 -------------------------
+#. Improvements to multi-threaded performance for small problems that
+   had regressed due to changes to threading (Dmitrity Korchemkin)
 #. Fix handling of M_PI for MSVC (Sergiu Deitsch)
 #. Add a default value for Solver::Summary::linear_solver_ordering_type (Sameer Agarwal)
 #. Make sure that the code compiles well with CUDA 11 (Dmitriy