Apple has again changed how its command line tools are packaged. Whereas it was once bundled into Xcode and then later you had to instead manually download it from within Xcode, it is now separated from Xcode altogether.
In some earlier versions of Xcode 5 you could run a command in the terminal and still get the download option to show up in Xcode but that no longer seems to be an option. At least as far as Xcode 5.1.
Now you need to download the command line tools from Apple’s developer site.