added a thank you to Martin Drohmann for his work on the howto

[[Imported from SVN: r245]]

doc/grid-howto.tex

@@ -101,6 +101,10 @@ of \Dune{} which is currently the most developed part. However, part of
 large variety of solvers for sparse linear systems) and a flexible class
 hierarchy for finite element methods. These will be described in
 subsequent documents. Now have fun!
+
+\vspace*{\fill}
+Thanks to Martin Drohmann for adapting this howto to version 1.2 of the
+DUNE grid interface.
 \end{abstract}
 
 \tableofcontents