Update argparse descriptions to make it clear that the script can also be used to compute MCC

[valosekj]

Checklist

GitHub

• I've given this PR a concise, self-descriptive, and meaningful title
• I've linked relevant issues in the PR body
• I've applied the relevant labels to this PR
• I've applied a release milestone (major, minor, patch) in line with Semantic Versioning guidelines
• I've assigned a reviewer

PR contents

• I've consulted SCT's internal developer documentation to ensure my contribution is in line with any relevant design decisions
• I've added relevant tests for my contribution
• I've updated the relevant documentation for my changes, including argparse descriptions, docstrings, and ReadTheDocs tutorial pages

Description

The sct_compute_compression function is meant to compute maximum spinal cord compression (MSCC) using the SC segmentation.
This PR updates the sct_compute_compression description to make clear that the function can also be used for maximum canal compromise (MCC) computation if spinal canal (aka CSF) segmentation is provided.
More context in #4330.

Currently, I have updated only the description (without changing any code). This assumes that users will read the description and will not provide spinal canal segmentation in combination with the -normalize-hc flag (normative database does not contain measures of the spinal canal). I made this clear by the following note:

spinalcordtoolbox/spinalcordtoolbox/scripts/sct_compute_compression.py

Lines 101 to 106 in 0ab1044

	'-normalize-hc',
	metavar=Metavar.int,
	type=int,
	choices=[0, 1],
	help='Set to 1 to normalize the metrics using a database of healthy controls. Set to 0 to not normalize. '
	'\nNote: This flag is valid only if the spinal cord segmentation is provided by the flag "-i".',

Linked issues

Resolves #4330

[joshuacwnewton]

Assuming the functionality works as intended, then I think the argparse changes are good!!

[joshuacwnewton]

((I just tweaked the title of the PR to make it clear that no new functionality is actually being added.))