Update doc and CHANGES.MD

Installation/CHANGES.md

@@ -37,6 +37,10 @@ Release History
    is given an optional template parameter `ConcurrencyTag` (default
    value remains `CGAL::Sequential_tag` for backward compatibility).
 
+### Surface Mesh
+
+ - The function `CGAL::Surface_mesh::clear()` now removes all non-default properties instead of just emptying them. 
+
 Release 5.0
 -----------
 

Surface_mesh/include/CGAL/Surface_mesh/Surface_mesh.h

@@ -1129,6 +1129,8 @@ public:
   }
 
     /// removes all vertices, halfedge, edges and faces. Collects garbage and clears all properties.
+    ///
+    /// After calling this method, the object is the same as a newly constructed object. The additional properties (such as normal vectors) are also removed and must thus be re-added if needed.
     void clear();