set manually:
-------------
- set python path in Makefile
- Makefile.systype simply defines which buildsystem to choose; no need to touch this file at all (note, all irrelevant Makefiles have been removed from buildsystem/)

- Config.sys:
   - this files controls most of the technical and some physical parameters of the code!
   - you may want/need to play with these settings

- buildsystem/:
   - set mpicxx compiler in buildsystem/Makefile.comp.gcc (should be the one installed in ../libraries/build/bin/)
   - set external libraries (FFTW, GSL, HDF5) in buildsystem/Makefile.gen.libs (again, should be the ones installed in ../libraries/build/)


peculiarity on macOS 12.4:
--------------------------
You need to 

setenv PATH /Users/aknebe/bin/gcc-9.2/bin/:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Library/TeX/texbin:/Library/Apple/usr/bin

before making Gadget4: mpich has been compiled with gcc-9 and so needs Gadget4 (note, mpicxx points uses the system-wide g++ as the backend, and we need to use the v9 one!)
