create help files for samplers

[florianhartig]

trafficstars

related to https://github.com/florianhartig/BayesianTools/issues/137, it ocurred to me that it would be good to have extra help files for the most important samplers, maybe one for the DE / DREAM family, and one for the Metropolis family, to show all the options, including stuff like restarts etc. that are specific for the samplers

[MaximilianPi]

Would it not be better to extend (and promote) our BT website ( sth like https://mlr-org.github.io/mlr/)? We could also add there some stuff about bayesian modelling (SEM, glmms...)