Update BETYdb documentation based upon install experience

[Chris-Schnaufer]

From @dlebauer

For documentation:

need to add record to machines table .e.g https://www.betydb.org/machines/25 need to set up dump.bety.sh cron job and dump_url .e.g. https://welsch.cyverse.org/pecan/dump/bety.tar.gz

From @gsrohde

Also for documentation: Fill in the remaining columns in the table at https://github.com/PecanProject/betydb-documentation/blob/bookdown/distributed_betydb.md.

[Chris-Schnaufer]

Refer to #616 for additional information [Edit - removed duplicate link to originating ticket]