Update CHANGELOG

Author: ThomasBarnekow

CHANGELOG.md

@@ -4,6 +4,10 @@ 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).
 
+## Version 2.11.0
+### Added
+- Added `OpenXmlElementFunctionalExtensions.With` extension methods, which offer flexible means for constructing `OpenXmlElement` instances in the context of pure functional transformations.
+
 ## Version 2.10.0
 ### Added
 - Added initial Office 2016 support, including `FileFormatVersion.Office2016`, `ExtendedChartPart` and other new schema elements (#586)