Sorry about that. Hadn't noticed that they updated that.
Go to the "APIs and Auth" area and then click on APIs. In there, you can enable the Google+ API.
Then, in the Registered Apps area, click into the app you created. At the bottom is a "REDIRECT URI" section. In there, enter the callback URLs as described in our Google documentation.
I hope that helps, and we'll get the doc updated shortly. If you have any questions or issues though, just let me know.
Thanks,
Alex