[handbook] first docu on dgf grid format

git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@15126 2fb0f335-1f38-0410-981e-8018bf24f1b0

doc/handbook/4_grids.tex

 \section{Grid Handling}
 \label{sec:gridhandling}
 
+This section summarizes some ideas about grid generation and grids that can be used by \Dumux. There are several external grid generates available which can be used. The output files of these generators need usually conversion into the Dune Grid Format (DGF), or some other format which can be read in by \Dune. We intend to give brief ideas how to work with external grids. However, this list is not complete.
+
 \subsection{DGF}
+Most of our \Dumux tests and tutorials use the Dune Grid Format (DGF) to read in grids. A detailed description of the DGF format and some examples can be found in the \Dune doxygen documentation \textbf{(Modules $\rightarrow$ I/O $\rightarrow$ Dune Grid Format (DGF)}). To generate larger or more complex DGF files, we recommend to write your own scripts, e.g in C++, Matlab or Python.
+
+The DGF format can also used to read in spatial parameters defined on the grid. These parameters can be defined on nodes as well as on the elements. An example for predefined parameters on a grid is the \texttt{test\_boxco2} or \texttt{test\_cco2} in the  \texttt{dumux/test/co2} folder.
+
+Inside \Dumux, the \texttt{DGFGridCreater} is set by default and doesn't need to be set your problem file.
 
 
 \subsection{GMSH}