[doxygen] Erroneous processing of installation doc
It seems that the script for cloning the DUNE modules on the website is displayed wrongly. It is
for module in common geometry grid localfunctions istl; do git clone -b releases/2.9 https://gitlab.dune-project.org/core/dune-\f$module.git done
It should be
for module in common geometry grid localfunctions istl; do git clone -b releases/2.9 https://gitlab.dune-project.org/core/dune-$module.git done
that means \f in front of $module is not necessary.