Update README.md

This app will help users when choosing books to read by providing them with additional information other than just their popularity in a fairly concise way. Just because a book is a bestseller does not mean it will necessarily be interesting to a particular reader, so the added information from these twitter users will help people determine whether a book would appeal to them personally, particularly if the Twitter user is someone whose tastes align with their own. In fact, this project could be expanded by accessing the app user's Twitter profile so that they get Twitter information on these books from people they actually follow (not just anyone who's tweeting about those books on Twitter.)