Add HDF description in IfcConvert

src/ifcconvert/IfcConvert.cpp

@@ -105,6 +105,7 @@ void print_usage(bool suggest_help = true)
         << "  .igs   IGES           Initial Graphics Exchange Specification\n"
         << "  .xml   XML            Property definitions and decomposition tree\n"
         << "  .svg   SVG            Scalable Vector Graphics (2D floor plan)\n"
+		<< "  .h5    HDF            Hierarchical Data Format storing positions, normals and indices\n"
 		<< "  .ifc   IFC-SPF        Industry Foundation Classes\n"
 		<< "\n"
         << "If no output filename given, <input>" << IfcUtil::path::from_utf8(DEFAULT_EXTENSION) << " will be used as the output file.\n";