Add the documentation header file draw_nef_3.h

Nef_3/doc/Nef_3/CGAL/draw_nef_3.h

@@ -0,0 +1,15 @@
+namespace CGAL {
+  
+/*!
+\ingroup PkgDrawNef3
+
+Open a new window and draws `anef3`, the `Nef_polyhedron_3`. A call to this function is blocking, that is the program continues as soon as the user closes the window. 
+ This function requires CGAL_Qt5, and is only available if the flag CGAL_USE_BASIC_VIEWER is defined at compile time.
+\tparam Nef3 a model of the `Nef_polyhedron_3` concept.
+\param anef3 the nef polyhedron to draw.
+
+*/
+template<class Nef3>
+void draw(const Nef3& anef3);
+
+} /* namespace CGAL */