Update free-programming-books.md

free-programming-books.md

@@ -884,6 +884,8 @@ See also [TeX](#tex)
 * [How To Think Like a Computer Scientist: Learning With Ruby](http://mysite.verizon.net/hpassel/thinkruby/)
 * [Ruby in Twenty Minutes](https://www.ruby-lang.org/en/documentation/quickstart/)
 * [Ruby Essentials](http://www.techotopia.com/index.php/Ruby_Essentials)
+* [Ruby User's Guide](http://www.linuxtopia.org/online_books/programming_books/ruby_guide/)
+* [Ruby Programming](http://www.linuxtopia.org/online_books/programming_books/ruby_tutorial/)
 * [Ruby Learning](http://rubylearning.com/)
 * [Try Ruby](http://tryruby.org/)
 * [Ruby Koans](http://www.rubykoans.com/)