Hi Pete,
Thanks for posting your question here.
In order to enter HTML code into the description editor, you will just need to click the "Source" button in the upper right corner. Once you have done so, you can click the "Source" button once more to get back to standard mode and view how the code displays.
If you need any further assistance with this, you are always welcome to contact our Customer Support team directly from under the “Help” tab within your account.
-Mike