add propertyEditorUis to extension types

Author: LanThuyNguyen

16/umbraco-cms/customizing/extending-overview/extension-types/README.md

@@ -93,6 +93,10 @@ The `tree` extension type is used to create a hierarchical structure composed of
 
 The `workspace` extension type provides functionality that operates within specific workspace environments, such as document editing, media management, or member editing.
 
+### [Property Editor UIs](../../../reference/property-editor-uis/README.md)
+The `PropertyEditorUi` extension type allows you to create custom property editors in the Umbraco backoffice.
+See the [official Umbraco documentation](../../../customizing/property-editors/README.md) for a guide on how to work with and create Property Editors.
+
 ## Even More Extension Types
 
 ### [Property Level UI Permissions](../../property-level-ui-permissions.md)