One more Dreamwidth Question

As I've previously said, I'm trying to go over to posting on Dreamwidth with everything re-posted here. At the moment Livejournal feels much more active for me, but I don't want to lose posts if things go pear-shaped here.

What I've noticed on other people's posts is that they have a link back to the Dreamwidth post, which looks like it's generated automatically. Can anyone tell me how to do that?