Add documentation for assign_wcs slit_y_low/slit_y_high parameters

[stscijgbot-jp]

Issue JP-3608 was created on JIRA by Kayli Glidic:

The assign_wcs step in the ReadTheDocs documentation would benefit from clearer explanations regarding its optional arguments for NIRSpec, particularly --slit_y_low and --slit_y_high, which define the height of the slit. Currently, the only documentation available is on the Step Arguments page, which states:

 

--slit_y_low (float, default=-0.55)

Lower edge of a NIRSpec slit.

--slit_y_high (float, default=0.55)

Upper edge of a NIRSpec slit.

 

It would be beneficial to specify in the documentation the units of these parameters, whether they represent slit units expressed as a fraction of the nominal slit height. This provide users with a better understanding of what values they might input if not the default. Additionally, it should also be documented outside the code somewhere to inform users that NIRSpec MOS slits automatically have an additional 0.5 margin added (from JP-3365), translating to a couple of pixels added at the top and bottom of the slit cutout.