Rework READMEs of 2021_Kuehn_et_al_Assessment_NPIs_Spatial and 2022_Koslow_et_al_Appropriate_Relaxation_NPIs

@mknaranja Could you have a look at the READMEs of 2021_Kuehn and 2022_Koslow? I already added the information of the simulations folder in MEmilio and some paper information. Maybe this is already enough. 
I don't think that we should provide an old commit hash, but maybe you have a different opinion.