Add some documentation

dune/fufem/improvegrid.hh

@@ -62,6 +62,11 @@ double aspectRatio(const EntityType& entity)
 
 }
 
+/** \brief Improve maximal aspect ratio of the grid by moving vertices.
+ *
+ *  \param grid The grid
+ *  \param threshold The threshold on the aspect ratio that determines which elements should be refined.
+ */
 template <class GridType>
 void improveGrid(GridType& grid, double threshold)
 {