src/pixie16/read/swettings/units.py file needs updating with current information

[Joe Henderson]

This file gives units for the different pixie variables and, to my knowledge, is obsolete. It would be nice to take the time and update the units to current known values

[Arun Persaud]

This file should probably stay this way, since it deals with the old setting file syntax… We should make sure though that we can still read the old settings file and perhaps have an option to convert it to the new one.

Should add at least add some doc string here that explains this.