add bson encoding performance to 4.5 changelog (#1336)

Author: sleepyStick

doc/changelog.rst

@@ -16,6 +16,7 @@ PyMongo 4.5 brings a number of improvements including:
   and :meth:`~pymongo.command_cursor.CommandCursor.try_next` to support
   executing an arbitrary command that returns a cursor.
 - cryptography 2.5 or later is now required for :ref:`OCSP` support.
+- Improved bson encoding and decoding performance by up to 134%(`PYTHON-3729`_, `PYTHON-3797`_, `PYTHON-3816`_, `PYTHON-3817`_, `PYTHON-3820`_, `PYTHON-3824`_, and `PYTHON-3846`_).
 
 Issues Resolved
 ...............
@@ -25,6 +26,14 @@ in this release.
 
 .. _PyMongo 4.5 release notes in JIRA: https://jira.mongodb.org/secure/ReleaseNote.jspa?projectId=10004&version=35492
 
+.. _PYTHON-3729: https://jira.mongodb.org/browse/PYTHON-3729
+.. _PYTHON-3797: https://jira.mongodb.org/browse/PYTHON-3797
+.. _PYTHON-3816: https://jira.mongodb.org/browse/PYTHON-3816
+.. _PYTHON-3817: https://jira.mongodb.org/browse/PYTHON-3817
+.. _PYTHON-3820: https://jira.mongodb.org/browse/PYTHON-3820
+.. _PYTHON-3824: https://jira.mongodb.org/browse/PYTHON-3824
+.. _PYTHON-3846: https://jira.mongodb.org/browse/PYTHON-3846
+
 Changes in Version 4.4.1
 ------------------------