Completed guess.rb Homework.

It took me a while to figure out a way to exit out of the program immediately when the user inputs a correct number. I first used return 0, but it gave me error: "ruby localjumperror unexpected return". Then I figured it out searching on google and used the "exit" method instead. 

Also I wasn't sure how often I should comment on our code. Is it appropriate to comment on each if statement?