Adds Building REST APIs with Rails book

free-programming-books.md

@@ -1530,6 +1530,7 @@ See also [TeX](#tex)
 * [Ruby on Rails 3.2 - Step by Step](http://www.xyzpub.com/en/ruby-on-rails/3.2/)
 * [Ruby on Rails 4.0 Guide](http://www.xyzpub.com/en/ruby-on-rails/4.0/)
 * [Upgrading to Rails 4](https://github.com/alindeman/upgradingtorails4)
+* [Building REST APIs with Rails](http://apionrails.icalialabs.com/book)
 
 
 ###Rust