* Add another Nim book to this list.

Add the Computer Programming with the Nim Programming Language book to this list.

* Update books/free-programming-books.md
Co-authored-by: NDavid Ordás <davorpatech@gmail.com>

* Update books/free-programming-books.md
Co-authored-by: NDavid Ordás <davorpatech@gmail.com>
Co-authored-by: NDavid Ordás <davorpatech@gmail.com>