Clarify parameter doc headers

[john-science]

What is the change? Why is it being made?

Our user docs looked like this:

But that is confusing because all of these "parameters" pages are parameter reports (list of parameters) EXCEPT the last one, which is a discussion of how mult parameters work, to put sub-block spatial grids of data into the ARMI reactor data model.

This confused ME, so I feel this is probably not clear enough.

Happily, this is an easy change. I change a header name and change the file name.

close #2381

SCR Information

Change Type: docs

One-Sentence Rationale: The header name for a section of the user docs was confusing.

One-line Impact on Requirements: NA

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Checklist

• [x] This PR has only one purpose or idea.
• [x] Tests have been added/updated to verify any new/changed code.
• [x] The documentation is still up-to-date in the doc folder.
• [x] The code style follows good practices.
• [x] The dependencies are still up-to-date in pyproject.toml.