Update CHANGELOG.md for 3.3 (#1887)

Co-authored-by: Michael Bowen <10384982+mikeebowen@users.noreply.github.com>

Author: twsouthwick

CHANGELOG.md

@@ -5,6 +5,19 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
+## [3.3.0] - 2025-03-06
+
+### Added
+
+- Added `DocumentFormat.OpenXml.Office.SpreadSheetML.Y2024.WorkbookCompatibilityVersion` namespace
+
+### Fixed
+- Performance of `.ToFlatOpc(...)` has been greatly improved for large parts (#1863)
+
+Thanks to the following for their contributions:
+
+@QuocDatHoang
+
 ## [3.2.0] - 2024-11-22
 
 ### Added