The trick is in the echo, which you may recall is dumping output to your browser, which can read HTML. So instead of
PHP Code:
echo "$name - $summary - $slug<br>";
You want to HTML-ize that up like so:
PHP Code:
echo "<p>$name - $summary - <a href='http://quidos.eventhq.co.uk/$slug'>$slug</a></p>";
As a side note, it's interesting you're using the DOMDocument Object to parse XML, when there are other tools in PHP better suited for parsing XML, such as the
SimpleXML object.