Add constraint not listed in Editor menu in Xcode
That documentation is incorrect.
Constraints are added via the buttons in the lower right corner of the Interface Builder workspace in Xcode 4.6:
The button on the left is for alignment-based constraints, and the middle one (the "I-beam") is for pinning spacing/heights.
In Xcode 5.0, those buttons look a little different, but the features are very similar:
