Document pipeline transformations applied by `UiLayer`

[yousefmoazzam]

From the signature of its single public method:

httomo/httomo/ui_layer.py

Line 50 in c7e399d

def build_pipeline(self) -> Pipeline:

it's clear enough that UiLayer is used to produce a Pipeline.

However, transforming pipeline data from some external format (eg, YAML) into a Pipeline is not all that it does, it makes some additional changes. These additional changes should be documented somewhere (possibly in the class docstring).

The only transformation it applies I think is taking side output references and inserting appropriate OutputRef objects into the parameter dicts of the relevant method wrappers.