docs: Simple filename mismatch fix in README

[tsturtz]

What:

Simple documentation change.

Why:

See line 177 for context as to why I'm submitting this. The file names are currently mismatched which is something I can see throwing people off.

How:

Markdown wizardry

Checklist:

• [x] Documentation
• [x] Tests
• [x] Updated Type Definitions
• [x] Ready to be merged