Update README.md

Author: rikba

README.md

@@ -91,6 +91,7 @@ In particular the dependencies are:
 - 2D Triangulation (GPL)
 - 2D Regularized Boolean Set-Operations (GPL)
 - 2D Straight Skeleton and Polygon Offsetting (GPL)
+- 2D Arrangement (GPL), see also `Fogel, Efi, Dan Halperin, and Ron Wein. CGAL arrangements and their applications: A step-by-step guide. Vol. 7. Springer Science & Business Media, 2012.`
 
 ### GTSP solver
 The underlying optimization uses the [memetic solver](http://www.cs.nott.ac.uk/~pszdk/?page=publications&key=Gutin2009a) presented in