doc update

doc/pypeit_par.rst

@@ -893,6 +893,7 @@ Key                       Type                                              Opti
 ``overscan_par``          int, list                                         ..                                                                   5, 65                          Parameters for the overscan subtraction.  For 'chebyshev' or 'polynomial', set overcan_par = order; for 'savgol', set overscan_par = order, window size ; for 'median', set overscan_par = None or omit the keyword.                                                                                                                                                                    
 ``rmcompact``             bool                                              ..                                                                   True                           Remove compact detections in LA cosmics routine                                                                                                                                                                                                                                                                                                                                         
 ``satpix``                str                                               ``reject``, ``force``, ``nothing``                                   ``reject``                     Handling of saturated pixels.  Options are: reject, force, nothing                                                                                                                                                                                                                                                                                                                      
+``scale_to_mean``         bool                                              ..                                                                   False                          If True, scale the input images to have the same mean before combining.                                                                                                                                                                                                                                                                                                                 
 ``scattlight``            :class:`~pypeit.par.pypeitpar.ScatteredLightPar`  ..                                                                   `ScatteredLightPar Keywords`_  Scattered light subtraction parameters.                                                                                                                                                                                                                                                                                                                                                 
 ``shot_noise``            bool                                              ..                                                                   True                           Use the bias- and dark-subtracted image to calculate and include electron count shot noise in the image processing error budget                                                                                                                                                                                                                                                         
 ``sigclip``               int, float                                        ..                                                                   4.5                            Sigma level for rejection in LA cosmics routine                                                                                                                                                                                                                                                                                                                                         
@@ -1115,6 +1116,12 @@ Alterations to the default parameters are:
               satpix = nothing
               use_pixelflat = False
               use_illumflat = False
+      [[slitless_pixflatframe]]
+          [[[process]]]
+              combine = median
+              satpix = nothing
+              use_pixelflat = False
+              use_illumflat = False
       [[scattlightframe]]
           [[[process]]]
               satpix = nothing