Merge pull request #255 from fernando-barajas/master

Add Ruby in Twenty Minutes and Ruby User's Guide

free-programming-books-es.md

@@ -44,6 +44,7 @@
 ###Ruby
 
 * [Guía para aprender a programar con Ruby. Adaptación al español del libro "Learn to Program" de Chris Pine](https://github.com/rubyperu/aprende.a.programar)
+* [Ruby en 20 minutos](https://www.ruby-lang.org/es/documentation/quickstart/)
 
 ###Haskell
 

free-programming-books.md

@@ -889,6 +889,7 @@ See also [TeX](#tex)
 * [Ruby Learning](http://rubylearning.com/)
 * [Try Ruby](http://tryruby.org/)
 * [Ruby Koans](http://www.rubykoans.com/)
+* [Ruby User's Guide](http://www.rubyist.net/~slagell/ruby/)
 
 
 ###Ruby on Rails