DOC: Update changelog

CHANGELOG.md

@@ -18,6 +18,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   See `build.properties.d/00_default.properties` for more information
 * Start editing an entity/creating a new record directly by adding an `#edit` or
   `#new_record` URI fragment, respectively.
+* Optional WYSIWYG editor with markdown output for text properties. Controled by
+  the `BUILD_MODULE_EXT_EDITMODE_WYSIWYG_TEXT` build variable which is set do
+  `DISABLED` by default.
 
 ### Changed (for changes in existing functionality)