update installation instructions for the 2023 course

README.md

@@ -19,9 +19,11 @@ The easiest way to install everything you need is to use the install scripts pro
 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 3.6 --dune-version 2.9
-python3 dumux/bin/installexternal.py dumux-course --dune-branch releases/2.9
+wget https://git.iws.uni-stuttgart.de/dumux-repositories/dumux/raw/master/bin/installdumux.py
+python3 installdumux.py --dumux-version master --dune-version 2.9
+cd dumux
+python3 dumux/bin/installexternal.py dumux-course --dumux-branch master --dune-branch releases/2.9
+./dune-common/bin/dunecontrol bexec rm -r CMakeFiles CMakeCache.txt
 ./dune-common/bin/dunecontrol --opts=./dumux/cmake.opts all
 ```
 
@@ -58,4 +60,4 @@ 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 3.6 in Dec 2022__.
+Last updated for: __DuMu<sup>x</sup> course 2023__.