Chat: add Message Editing demo description (DevExpress#29943)

Author: vladaskorohodova

apps/demos/Demos/Chat/MessageEditing/description.md

@@ -1,3 +1,8 @@
-In our upcoming major release (v25.1) our Chat component will allow users to edit/delete messages once they’ve been sent. 
+The Chat component allows users to edit and delete sent messages.
+
+Use a [data source](/Documentation/ApiReference/UI_Components/dxChat/Configuration/#dataSource) if you want users to edit and delete messages. Implement custom insert, update, and delete operations. Once you configured these operations, enable [editing](/Documentation/ApiReference/UI_Components/dxChat/Configuration/editing/).
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-DevExtreme Chat is a client-side component that requires a backend solution. Message editing and delete operations will include relevant UI elements for end users and APIs to modify rendered messages. To edit and remove messages from a data source, you will need to use Push APIs. 
+
+The **editing** object includes [allowUpdating](/Documentation/ApiReference/UI_Components/dxChat/Configuration/editing/#allowUpdating) and [allowDeleting](/Documentation/ApiReference/UI_Components/dxChat/Configuration/editing/#allowDeleting) properties. These Boolean options are initially `false`. You can set them to `true` or use functions with custom logic. When options are `true`, users can edit/delete their own messages.
+
+In this demo, try deleting or editing messages. First, check that the options are active in the panel next to the Chat component. Right-click or long-tap a message to access the "Edit" and "Delete" commands in the context menu. Edit a message in the input field and click "Send" to save changes.