[DOC] Minor updates to software paper for JOSS review

[emdupre]

Summary

Relates to https://github.com/openjournals/joss-reviews/issues/6434

Describe your changes

Minor updates to the software paper accompanying the JOSS submission for MapReader for readability and formatting.

Checklist before assigning a reviewer (update as needed)

• [ ] Self-review code
• [ ] Ensure submission passes current tests
• [ ] Add tests
• [ ] Update relevant docs

Reviewer checklist

Please add anything you want reviewers to specifically focus/comment on.

• [ ] Everything looks ok?