How do I use this web API to check if an username is taken or no?

I am making an username generator. It generates an username every 0.1 second. If the username is not taken then it will print the username, else it won't do anything. I do not understand how you use this web API which can be used for that.

http://www.roblox.com/UserCheck/DoesUsernameExist?username=test

Can anyone help?

(Example)

Lets say I have a username.

local username = "bimorp"

Now I want to check if that username exists. If it does it won't do anything. If it doesn't it will print it.