Added the 'Why programmers work at night' book to the 'Professional Development' list.

free-programming-books.md

@@ -412,6 +412,7 @@
 * [How to be a Programmer: A Short, Comprehensive, and Personal Summary](http://samizdat.mines.edu/howto/HowToBeAProgrammer.html) by Robert L. Read
 * [How to Do What You Love & Earn What You’re Worth as a Programmer](https://leanpub.com/dowhatyoulove/read) *(Leanpub, By Reginald Braithwaite)*
 * [What I've Learned From Failure](https://leanpub.com/shippingsoftware/read) *(Leanpub, By Reginald Braithwaite)*
+* [Why programmers work at night](https://leanpub.com/nightowls/read) *(Leanpub, By Swizec Teller)*
 
 ####Programming Paradigms
 * [Introduction to Functional Programming](http://www.cl.cam.ac.uk/teaching/Lectures/funprog-jrh-1996/) (class lectures and slides)