Added three links for students

I have added three links that Students might find useful. They are Citation Machine Quizlet Purdue OWL: Online Writing Lab . Citation Machine is a Citation generator, Quizlet allows you to create your own study guides/practices quizzes, and Purdue OWL teaches you various ways to cite in different styles (teaches you how to NOT plagiarize. Very important in the academic world, especially if you don't fancy being expelled from your university or sued.)