Xcode 9 now allows wireless debugging, so it's not mandatory to connect your device with a cable anymore. 🎉

Note this also includes wireless debugging with tvOS (tvOS 11.0+). This is great as you can now keep your Apple TV plugged into your TV set in one room while working on Xcode in another room. From the Xcode 9 GM release notes:

iOS devices and Apple TV can now be debugged over the network. For more information, see the topics in Xcode Help > Run and debug > Network debugging. (10968305)

For the initial pairing, you just need the Mac that runs Xcode and the Apple TV on the same wireless network. Open the "Devices and Simulators" window in Xcode. Then on the Apple TV, go to Settings > Remotes and Devices > Remote App and Devices. Now go back to the Xcode devices window and select the discovered Apple TV in the sidebar. Finally, a verification number will appear on the Apple TV, which you can then enter in Xcode to pair.