It says to use the "edit URL" in the code itself, but I couldn't see
where to get that URL from. When I downloaded the mail into VM, it
showed up as an Ical event.
Here is how I use this in my own environment, your usage might
vary depending on how you use g-client.
0) I use xslt to preview the atom feed as XHTML and have Emacs
render it (either via w3 or w3m).
1) I grab the url under the "edit" link into the kill ring,
and paste it in the minibuffer when accepting the event.
Hope this helps,