Enhance form field count readme

[ChaseMillers]

PR Description:

I only updated the README.mb file linked to the Form Field Count.js file.
This new README.md explains more about what the actual .js file does as well as how to use.
The .js code itself doesn't have much comments to explain, so this change seemed helpful and appropriate.

Pull Request Checklist

Overview

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Code Quality

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Documentation

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[ravichandra1998g]

Approved