[handbook] Update external modules list

doc/handbook/2_detailedinstall.tex

@@ -281,6 +281,17 @@ and some more libraries and tools which are prerequisites for their use.
   of choice for simulating structures such as foams, discrete fracture networks,
   or network flow problems.
   Download: \url{https://gitlab.dune-project.org/extensions/dune-foamgrid}
+  
+\item \textbf{opm-grid}: opm-grid is a DUNE module supporting grids in a corner-point format.
+  Download: \url{https://github.com/OPM/opm-grid.git}
+  
+\item \textbf{dune-subgrid}: The dune-subgrid module allows to mark elements of another hierarchical dune grid.
+The set of marked elements can then be accessed as a hierarchical dune grid in its own right.
+Dune-Subgrid provides the full grid interface including adaptive mesh refinement.
+  Download: \url{https://git.imp.fu-berlin.de/agnumpde/dune-subgrid.git}
+  
+\item \textbf{dune-spgrid}: The DUNE module dune-spgrid provides a structured, parallel grid.
+  Download: \url{https://gitlab.dune-project.org/extensions/dune-spgrid.git}
 
 \item \textbf{SuperLU}: External library for solving linear equations. SuperLU is a general purpose
   library for the direct solution of large, sparse, non-symmetric systems of linear equations.