Update Highrise section

[Simon Williams]

Hey all, love what you're doing, thanks for making this resource public to help others get insight into how you run things.

Was just going through it after watching a GettingReal video, and noticed that the highrise section needs to be updated in light of the recent closure to new signups.

Thanks again!

[David Heinemeier Hansson]

Thanks for the prodding! I've updated the section in e492a89.