Technically you can add a line break in your description by adding one whitespace after your first line, adding an entire line of non-whitespace characters (enough to force a newline), adding one whitespace after that, and then adding your next line.
<description>First line ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ Second line</description>
This gives me:
First line
-------------------------------------------------------------------------------------------------------------
Second line
(Looks better in Splunk)
It's not elegant, and is going to give you resizing/browser problems, but Splunk's SimpleXML was designed by a 5 year old, so
