This is the point:
You have not agreed to the Xcode license agreements, please run
'xcodebuild -license'
(for user-level acceptance) or'sudo xcodebuild -license'
(for system-wide acceptance) from within a Terminal window to review and agree to the Xcode license agreements.
This is a one-time thing you have to to, so I didn't remember about it before. I'm surprised anyway that this issue isn't stated anywhere in the website.