Merge branch 'update-to-dumux-3.6' into 'master'

Make dumux course 3.6 work with dumux release 3.6

See merge request !132

README.md

@@ -20,8 +20,8 @@ for instance, with this sequence of commands:
 
 ```bash
 wget https://git.iws.uni-stuttgart.de/dumux-repositories/dumux/raw/releases/3.5/bin/installdumux.py
-python3 installdumux.py --dumux-version 3.5 --dune-version 2.8
-python3 dumux/bin/installexternal.py dumux-course
+python3 installdumux.py --dumux-version 3.6 --dune-version 2.9
+python3 dumux/bin/installexternal.py dumux-course --dune-branch releases/2.9
 ./dune-common/bin/dunecontrol --opts=./dumux/cmake.opts all
 ```
 
@@ -58,4 +58,4 @@ software packages are needed:
 For some excercises you might need UMFPack. UMFPack can be installed via Suitesparse.
 For instance on Ubuntu use `apt-get install libsuitesparse-dev`.
 
-Last updated for: __DuMu<sup>x</sup> release 3.5 in May 2022__.
+Last updated for: __DuMu<sup>x</sup> release 3.6 in Dec 2022__.