DOC: update new_instrument instructions for pysat.Meta.from_csv

[aburrell]

Is your feature request related to a problem? Please describe.
I can't think of any instance where I've used pysat.Meta.from_csv in an Instrument sub-module, but it is presented as an option in the new_instrument documentation instructions. I have no idea how this would work, so the instructions need to be expanded.

Describe the solution you'd like
Better instructions on how to use the pysat.Meta.from_csv method in an Instrument sub-module.

Describe alternatives you've considered
Remove the reference to ``pysat.Meta.from_csv`

Additional context
Encountered in #1110, but didn't receive feedback at the time.