Document transition from custom resp-belt to biopac one

[bpinsard]

Will need to be documented when releasing the physio data.

[julieaboyle1]

@bpinsard , I think the best way to do is to update the information during the next release. At the moment, all datasets included in the 2022 release were acquired with the custom respiration belt. What do you think? The division will definitely need to be documented and in a prevalent place in the docs when we release physio data

[bpinsard]

If we consider the last seasons of Friends, a good portion of the release uses the new resp belt.

[bpinsard]

But we don't ship any physio data in the release, so it doesn't really matter.