document device_id

[sneakers-the-rat]

i think we probably want to make use of this in a few places, some unique identifier for a device, so let's document how it works or otherwise link to where it gets documented in the firmware docs from the docs here.

from: #48 (comment)

It's just a number burned into the firmware and nothing OS-related (similar to serial number in SCPI instruments). It's used to filter out commands sent to a specific Miniscope when there are several scopes in one experiment.

[t-sasatani]

The firmware is not really documented, but posting anyways. The definition is here. Agree we should come back here soon.
https://github.com/Aharoni-Lab/Miniscope-SAMD-Framework/blob/13fbb85c114ac290a462bda1250c6406384c9acb/include/MS_config.h#L74

[t-sasatani]

and this is used here to screen commands that come to the specific device.
https://github.com/Aharoni-Lab/Miniscope-SAMD-Framework/blob/13fbb85c114ac290a462bda1250c6406384c9acb/src/MS_callback.c#L119