Added the 'Kanban for skeptics' book to the 'Software Architecture' list.

free-programming-books.md

@@ -452,6 +452,7 @@
 * [The Definitive Guide to Building Code Quality](http://nexus.realtimepublishers.com/dgbcq.php)
 * [Web API Design](https://blog.apigee.com/detail/announcement_new_ebook_on_web_api_design)
 * [Your API Is Bad](https://leanpub.com/yourapiisbad) *(Leanpub, by Paddy Foran)*
+* [Kanban for skeptics](https://leanpub.com/kanbanforskeptics) *(Leanpub, by Nick Oostvogels)*
 
 ####Standards
 * [UNIX - The POSIX Standard - IEEE Std 1003.1](https://github.com/g-nix/posix-standard)