[Feature]: Allow specifying unit in `ElectricalSeries` about pynwb HOT 1 OPEN

Hi @susiefeng,

You can store your data in any units of voltage and then set the conversion field of your ElectricalSeries to be the value that you have to multiply your data with to get the data into volts. So if the values of data are stored in mV, then conversion should be 1e-3. For uV, it should be 1e-6.

We recommend that you store your voltage data in its most raw form -- the integer values returned from the analog-to-digital converter. This can save storage space, because probably your data will be in int16 instead of float64. The converter or acquisition system should provide by a conversion factor that you need to multiply your raw data by to get your data into units of V or mV (e.g., 1.95e-7 to convert Intan data into volts). That's the value you would put into the conversion field. Let me know if you have any questions.

from pynwb.