I realize that is a command but where do I type it? In the google searchbox? Do I enter it into my browser address bar? Jokes aside, does every major OS accept the same command? What platform is this command for? Why is it not obvious from the article what type of system that command is for?
You add it to the command line you use to launch the bitcoin program. If you use a shortcut on Windows, you can set the command line in the properties. (Shortcut -> Target)
I'm not sure why it's not an RPC command too. It really should be.