Xonotic launch error on macOS

Xonotic is a free and open-source first-person shooter video game. When launching from Xonotic.app, it reports the following error message.

You have reached this menu due to missing or unlocatable content/data. You may consider adding -basedir /path/to/game to your launch commandline.

Setup:

Solution: Run the game from command line.

Spotlight search -> Terminal

cd ~/Downloads/Xonotic/Xonotic.app/Contents/MacOS
open xonotic-osx-sdl-bin