docs(multiple-checkboxes): add disableOthers to option config docs

[matyasjay]

Description

• This option is missing from the docs and could be discovered only by walking through the source code. It is now documented in the main README.md file

Related Issue

N/A

Motivation and Context

• Tired of checking source code all the time for the exact name

How Has This Been Tested?

I don't think it has to be tested in any way but let me know.

Screenshots (if appropriate):

Types of changes

• 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 change)
• Docs

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.