1st time user doc

We need to improve the documentation to the first-time user - right now we have essentially delegated this to the Tutorials.

Specific suggestions:

• remove MAC from configure.sh and documentation
• in configure.sh: " To compile your program use: 'make TARGET' " --> remove "TARGET"
• in configure.sh: " Activating fallback option with gfortran for SERIAL JOB." --> ADD "Deactivating MPI"
• add compiler names (e.g., ifort) to the documentation and/or configure.sh script
• mention again the repository URL and add to the documentation instructions on how to download a branch from Gitlab
• later on (after the changes to 2.0 are agreed on) reproduce them in 2.1 (option: git cherrypick)
• include some of the changes from branch 184 - https://git.physik.uni-wuerzburg.de/-/ide/project/ALF/ALF/tree/184-pgi-compiler-bug/-/Makefile/
• add table/list with (a basic shell) step for step instructions to get a number (energy) from ALF to the documentation, including cat $file, based on the tutorial