Add a book about Geometry Algorithms by Dan Sunday (#2804)

* Add a book about Geometry Algorithms by Dan Sunday

* remove / from url to satisfy linter

free-programming-books.md

@@ -294,6 +294,7 @@
 * [Data Structures Succinctly Part 2, Syncfusion](https://www.syncfusion.com/resources/techportal/ebooks/datastructurespart2) (PDF, Kindle) *(Just fill the fields with any values)*
 * [Elementary Algorithms](https://github.com/liuxinyu95/AlgoXY) - Larry LIU Xinyu
 * [Foundations of Computer Science](http://infolab.stanford.edu/~ullman/focs.html) - Al Aho and Jeff Ullman
+* [Geometry Algorithms](http://geomalgorithms.com) - Dan Sunday
 * [Handbook of Graph Drawing and Visualization](https://cs.brown.edu/~rt/gdhandbook/)
 * [Lectures Notes on Algorithm Analysis and Computational Complexity (Fourth Edition)](https://larc.unt.edu/ian/books/free/license.html) - Ian Parberry (use form at bottom of license)
 * [LEDA: A Platform for Combinatorial and Geometric Computing](http://people.mpi-inf.mpg.de/~mehlhorn/LEDAbook.html) - K. Mehlhorn et al.