chore: Added note to notifications.md (#10223)

Added a note underneath the 'writing the message' heading for using markdown in notifications.

Author: mattyforth

notifications.md

@@ -831,6 +831,9 @@ Thanks,<br>
 </x-mail::message>
 ```
 
+> [!NOTE]  
+> Do not use excess indentation when writing Markdown emails. Per Markdown standards, Markdown parsers will render indented content as code blocks.
+
 <a name="button-component"></a>
 #### Button Component