Add "Learn Ruby the Hard Way" by Zed A. Shaw (#5842)

books/free-programming-books-langs.md

@@ -1977,6 +1977,7 @@ That section got so big, we decided to split it into its own file, the [BY SUBJE
 * [Introduction to Programming with Ruby](https://launchschool.com/books/ruby) - Launch School
 * [Just Enough Ruby to Get By](http://jasonkim.ca/projects/just_enough_ruby_to_get_by/)
 * [Learn Ruby First](https://essenceofchaos.gitbooks.io/learn-ruby-first/content/) - Frederick John
+* [Learn Ruby the Hard Way](https://learnrubythehardway.org/book/) - Zed A. Shaw
 * [Learn to Program](http://pine.fm/LearnToProgram/) - Chris Pine
 * [Mastering Roda](https://fiachetti.gitlab.io/mastering-roda) - Federico Iachetti, Avdi Grimm and Jeremy Evans
 * [Mr. Neighborly's Humble Little Ruby Book](https://web.archive.org/web/20180321101922/http://www.humblelittlerubybook.com/book/html/index.html)