Merge pull request #19 from demands/patch-1

Add DTrace book from illumos

free-programming-books.md

@@ -11,6 +11,7 @@
 * [Clojure](#clojure)
 * [CoffeeScript](#coffeescript)
 * [ColdFusion](#coldfusion)
+* [D / DTrace](#d--dtrace)
 * [DB2](#db2)
 * [Delphi / Pascal](#delphi-pascal)
 * [Django](#django)
@@ -232,6 +233,8 @@
 
 * [CFML In 100 Minutes](https://github.com/mhenke/CFML-in-100-minutes/blob/master/cfml100mins.markdown)
 
+###D / DTrace
+* [IllumOS Dynamic Tracing Guide](http://dtrace.org/guide/preface.html)
 
 ###DB2