[!377] Documents the fact that ConvectionDiffusionDG does not work with degree 0
Merge branch 'documentation/convectiondiffusionDG' into 'master'
See merge request pdelab/dune-pdelab!377
(cherry picked from commit b97e9f46)
8f25b4ef Documents the fact that ConvectionDiffusionDG does not work with degree 0 finite element maps.