[NL] removed comment, added docu

NumLib/Fem/CoordinatesMapping/NaturalCoordinatesMapping.h

@@ -21,6 +21,7 @@ namespace NumLib
 {
 namespace detail
 {
+//! Used to explicitly instantiate the NaturalCoordinatesMapping class template.
 template <class T_MESH_ELEMENT,
           class T_SHAPE_FUNC,
           class T_SHAPE_MATRICES,
@@ -83,7 +84,4 @@ struct NaturalCoordinatesMapping
 
 } // NumLib
 
-// #include "NaturalCoordinatesMapping-impl.h"
-
-
 #endif //NATURALCOORDINATESMAPPING_H_