Add Yet Another Introductory Number Theory Textbook to free-programming-books.md (#5015)

* Add Free and Open Machine Learning book to free-programming-books.md

* Add Resilient Web Design to free-programming-books.md

* Add Lies, Damned Lies, or Statistics: How to Tell the Truth with Statistics Book to free-programming-books.md

* Add Scientific Computing Book to free-programming-books.md

* Add Signal Computing: Digital Signals in the Software Domain Book to free-programming-books.md

* Add  Book to free-programming-books.md

free-programming-books.md

@@ -583,6 +583,7 @@
 * [The Joy of Cryptography (2020)](https://web.engr.oregonstate.edu/~rosulekm/crypto/) - Mike Rosulek (PDF) (:construction: *in process*)
 * [Think Bayes: Bayesian Statistics Made Simple](http://www.greenteapress.com/thinkbayes/) - Allen B. Downey
 * [Think Stats: Probability and Statistics for Programmers](http://greenteapress.com/thinkstats/) - Allen B. Downey (using Python)
+* [Yet Another Introductory Number Theory Textbook](https://www.poritz.net/jonathan/share/yaintt.pdf) - Jonathan A. Poritz (PDF)
 
 
 #### Mathematics For Computer Science