Update free-programming-books.md

added javascript's http://devdocs.io/

free-programming-books.md

@@ -564,6 +564,7 @@
 * [The JavaScript Tutorial](http://javascript.info/)
 * [AngularJS in 60 Minutes](http://fastandfluid.com/publicdownloads/AngularJSIn60MinutesIsh_DanWahlin_May2013.pdf) (PDF)
 * [Javascript Succinctly, Syncfusion](http://www.syncfusion.com/resources/techportal/ebooks/javascript) (PDF, Kindle) *(Just fill the fields with any values)*
+* [Dev Docs](http://devdocs.io/)
 
 ####Backbone.js