Section on tools for extracting physio signal from imaging data

[tsalo]

Summary

Per this week's call, we want to document related research areas, including tools for extracting physio signal from fMRI data, in the physiopy documentation.

Additional detail

Some papers on extracting physio signals:

• Salas et al. (2020)
• Hocke & Frederick (2020)
• Aslan et al. (2019)

Next Steps

1. Add documentation on unsupported tools/algorithms for extracting physio signal to "related tools" section.