Updating the beast_settings documentation

[cmurray-astro]

It looks like the beast settings documentation (https://beast.readthedocs.io/en/latest/beast_setup.html#) needs an update to include all required parameters and to remove out-of-date parameters. It is also clear that this file needs to be reconciled with the more-detailed descriptions of the parameters, e.g., the artificial star input list parameters (https://beast.readthedocs.io/en/latest/beast_setup.html#)