add book in Theoretical Computer Science Subject (#7627)

add book in Theoretical Computer Science Subject - Creative commons freely avalaible online, check footer

books/free-programming-books-subjects.md

@@ -827,6 +827,7 @@ Kerridge (PDF) (email address *requested*, not required)
 * [Structure and Interpretation of Computer Programs](https://sarabander.github.io/sicp/html/index.xhtml) - Harold Abelson, Gerald Jay Sussman, Julie Sussman (HTML)
 * [The Black Art of Programming](http://self.gutenberg.org/wplbn0002828847-the-black-art-of-programming-by-mcilroy-mark.aspx?) - Mark McIlroy
 * [The Craft of Programming](https://kilthub.cmu.edu/articles/The_Craft_of_Programming/6610514) - John C. Reynolds
+* [The Nature of Code](https://natureofcode.com/book) - Daniel Shiffman (HTML)
 * [Theory of Computation, Making Connections](https://joshua.smcvt.edu/computation) - Jim Hefferon (PDF)
 * [Think Complexity](https://greenteapress.com/wp/think-complexity-2e/) - - Allen B. Downey (2nd Edition) (PDF, HTML)