docs: add CSS debugging method and small Node.js note to README

[cengizilhan]

Description

Adds a CSS debugging method to help inspect the dropdown open state more easily.
Also includes a small Node.js-related note for clarification.

This improves developer experience by making debugging steps clearer in the README.

Screenshots (if appropriate)

N/A

Types of changes

• Chore (tooling change or documentation change)
• Refactor (non-breaking change which maintains existing functionality)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• My code follows the code style of this project.
• I have added new tests for the bug I fixed/the new feature I added.
• I have modified existing tests for the bug I fixed/the new feature I added.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.