Document the location of the wavefront calculation in Algorithm.py - find whether `zer4UpNm` https://github.com/lsst-ts/ts_wep/blob/d41a81fe380c09432950d0db933e7b664b8782ea/python/lsst/ts/wep/cwfs/Algorithm.py#L785 is calculated at the location of the donut, or at the center of the detector. ts_ofc only requires the detector-averaged quantity. This ticket is to create a notebook / TN documenting the Algorithm.