add TODO imformation

README.md

@@ -19,7 +19,7 @@ In the modules root directory. Required dependencies are the modules
 - dune-common
 - dune-grid
 
-and optionally you may provide different grid modules that can be used with
+and optionally you may provide various grid modules that can be used with
 dune-multimesh, e.g.
 - dune-alugrid
 - dune-foamgrid
@@ -36,7 +36,7 @@ using HostGrid = ALUGrid<2, 2, simplex, conforming>;
 MultiMesh<HostGrid> multimesh(2);
 ```
 
-If the host-grid allows to pass arguments to its constructo, these can be
+If the host-grid allows to pass arguments to its constructor, these can be
 appended to the MultiMesh constructor after the size argument, e.g.
 
 ```c++
@@ -47,10 +47,10 @@ MultiMesh<HostGrid> multimesh(2, filename);
 Since grids are not copy-constructable, all grids in a MultiMesh are constructed
 from scratch from the same arguments or the same grid-factory, to guarantee
 that the coarse-grid level is the same in all grids. When using a `GridFactory`
-with MultiMesh, it is required to set the number grids to create in the
+with MultiMesh, it is required to set the number of grids to create in the
 GridFactory constructor. This is different to other GridFactories. The default-
 constructor creates one grid only. (This is just to be conform the the
-GridFactory interface). In order to use, e.g. structured grid-factory builders,
+GridFactory interface). In order to use, e.g., structured grid-factory builders,
 you have to pass the MultiMesh GridFactory:
 
 ```c++
@@ -63,3 +63,14 @@ auto gridPtr = Factory::createSimplexGrid(gridFactory, lower, upper, num);
 Since the dune-grid StructuredGridFactory does not allow to pass an own
 GridFactory object to fill, a modified StructuredGridFactory is provided in the
 utility folder, called `StructuredGridBuilder`.
+
+TODO
+----
+The current implementation is very limited. Several things need to be
+implemented:
+- Parallelization, especially load-balance for more than one grid
+- Abstraction of the MultiEntity. Currently its just a vector of entities. It
+  would be better to have an order relation, e.g. by grid-level, to allow for a
+  fast access to the smallest and largest entity.
+- Provide Interpolation / hierarchic Geometry-Objects, like the geometryInFather
+  for father-child relations.