Hey, there's a setting for this kind of thing!

It's under Settings > Edit Profile Information > Streaming Status. You can set the URL of the stream there, give it a description, and there's a little drop-down box that informs everyone watching you that you'll be streaming soon, or are streaming right now! It's a little different, but it might be useful~

Really? I think I think I tried it but dunno if it worked, haha.