Sorry I missed this, but to do it you'll see at the end on your final score it says:
"share your score with the url:" or "let others challenge your score with the url:"
You just copy and paste the url next to one of these, which is a wee bit on the massive size, for example
my score. However I've noticed they time out after a while so don't know how useful it is.
[edit] Seems that didn't work after all, or the system is temporarily unavailable.
Edited by Malcolm, : No reason given.