adding another tour of scala

free-programming-books.md

@@ -573,6 +573,7 @@
 * [Scala By Example](http://www.scala-lang.org/docu/files/ScalaByExample.pdf) (PDF)
 * [A Scala Tutorial for Java programmers](http://www.scala-lang.org/docu/files/ScalaTutorial.pdf) (PDF)
 * [Xtrace](http://github.com/leithaus/XTrace/tree/monadic/src/main/book/content/)
+* [Another tour of Scala](http://naildrivin5.com/scalatour)
 
 
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