Add a table that describes the data output by various hardware

[cjsha]

Something like this:

except the focus would be hardware, i.e. it wouldn't include so much information about OpenEphys.Onix1 nodes.
It would include conversion factors not just for ephys streams but also aux adc and other streams that need to be converted per this comment

I would suggest adding it to this page or a reference page in the same section of the docs

[ChucklesOnGitHub]

Update signal processing tutorial accordingly once this is done.