Slightly improve PhotoCalTask docs

PhotoCalTask.run was returning important items that were
not documented. I added incomplete info.

python/lsst/pipe/tasks/photoCal.py

@@ -589,6 +589,8 @@ def run(self, exposure, matches, doSelectUnresolved=True):
          - calib -------  \link lsst::afw::image::Calib\endlink object containing the zero point
          - arrays ------ Magnitude arrays returned be PhotoCalTask.extractMagArrays
          - matches ----- Final ReferenceMatchVector, as returned by PhotoCalTask.selectMatches.
+         - sigma ------- ?standard deviation of fit of zero point?
+         - ngood ------- ?number of sources used to fit zero point?
 
         The exposure is only used to provide the name of the filter being calibrated (it may also be
         used to generate debugging plots).