Add PAIP book (#2922)

free-programming-books.md

@@ -1702,6 +1702,7 @@ Kerridge (PDF) (email address *requested*, not required)
 * [Lisp Koans](https://github.com/google/lisp-koans)
 * [Lisp Web Tales](https://leanpub.com/lispwebtales) - Pavel Penev *(Leanpub account or valid email requested)*
 * [On Lisp](http://www.paulgraham.com/onlisp.html) - P. Graham
+* [Paradigms of Artificial Intelligence Programming: Case Studies in Common Lisp](https://github.com/norvig/paip-lisp) - Peter Norvig (PDF, epub, markdown)
 * [Practical Common Lisp](http://www.gigamonkeys.com/book/) - P. Seibel
 * [Successful Lisp: How to Understand and Use Common Lisp](https://github.com/clojurians-org/lisp-ebook/blob/master/Successful%20Lisp%20How%20to%20Understand%20and%20Use%20Common%20Lisp%20-%20David%20B.%20Lamkins.pdf) - David Lamkins (PDF)
 * [The Common Lisp Cookbook](https://lispcookbook.github.io/cl-cookbook/)