HTML Editor: update Markdown Support demo description (#28429)

apps/demos/Demos/HtmlEditor/MarkdownSupport/description.md

@@ -1,4 +1,6 @@
-Our HtmlEditor outputs the markup in HTML format.
+DevExtreme HTML Editor uses HTML markup to format its document content. This demo module converts content to Markdown with the help of the [unified](https://github.com/unifiedjs/unified) plugin library.
 
-The HtmlEditor stores the markup in the [value](/Documentation/ApiReference/UI_Components/dxHtmlEditor/Configuration/#value) property. In this demo, the value is displayed under the HtmlEditor.
+The code sets the the editor's [converter](/Documentation/ApiReference/UI_Components/dxHtmlEditor/Configuration/converter/) property to an object that implements two functions: [toHtml](/Documentation/ApiReference/UI_Components/dxHtmlEditor/Configuration/converter/#toHtml) and [fromHtml](/Documentation/ApiReference/UI_Components/dxHtmlEditor/Configuration/converter/#fromHtml). 
+
+Try to edit or format text in the HTML Editor control and see how the Markdown Preview section reflects those changes. 
 <!--split-->