Thank you for your reply.
To add a description in the property grid you can add a third column in the data table with the description text. You can then add a Description attribute with the text from that column in the constructor of the custom property descriptor in this example named "MyPropertyDescriptor". I have made these changes in the example and I have added a comment which starts with "//DESCRIPTION" in the places I have made changes. There are a total of three modifications that you can quickly navigate to by searching for the above comment start.
If you have further questions, feel free to write back.
the Telerik team