Add OO programming with Ruby book

free-programming-books.md

@@ -1870,6 +1870,7 @@ For resources on Angular, Backbone, D3, Dojo, Ember, Express, jQuery, Knockout,
 * [Learn Ruby the hard way](http://learnrubythehardway.org/book/)
 * [Learn to Program, by Chris Pine](http://pine.fm/LearnToProgram/)
 * [Mr. Neighborly's Humble Little Ruby Book](http://www.humblelittlerubybook.com)
+* [Object Oriented Programming with Ruby](https://launchschool.com/books/oo_ruby) - Launch School
 * [Practicing Ruby](https://github.com/elm-city-craftworks/practicing-ruby-manuscripts)
 * [Programming Ruby](http://ruby-doc.com/docs/ProgrammingRuby/)
 * [Ruby Essentials](http://www.techotopia.com/index.php/Ruby_Essentials)