Change the wording of the known issue

Author: Leah-Xia-Microsoft

articles/communication-services/concepts/ui-library/includes/web-ui-use-cases.md

@@ -143,7 +143,7 @@ Localization is key to making products for users around the world and who speak
 
 ## Known Issues
 
-* The UI library doesn't support adding rich text formatting to existing messages that have a ChatMessageType of 'text' at this time.
+* The UI library doesn't support updating message type when editing the existing messages at this time. Adding rich text formatting to an existing message will add html styling to the text content but not changing the message type. This may result in displaying html content as plain text in the message thread.
 
 > [!div class="nextstepaction"]
 > [Visit UI Library storybook](https://azure.github.io/communication-ui-library)