Document that you need to require rspec-prof somewhere

[Lykos]

Hello,

this seems very obvious, but I tried to follow your documentation and just couldn't get it to work. Eventually I figured out I have to add require 'rspec-prof' somewhere and added that to my spec_helper.

Maybe update your documentation to explicitly state that. It may seem obvious, but if you just blindly follow the documentation, you will run into this problem and I think I am not the only one who has run or will run into this.