fix: inconsistent property names in treasure-hunter

[JoshuaKGoldberg]

PR Checklist

• [x] Addresses an existing open issue: fixes #222
• [x] That issue was marked as accepting prs
• [x] Steps in CONTRIBUTING.md were taken

Overview

Corrects the property names (and description of interface/type) in the README.md to match the intended solution. I think the code has better names.