Update index.html

[NoguchiMasafumi]

I have always found your service to be very convenient. However, I have noticed that sometimes when I paste text, it can be difficult to read. Therefore, I would like to suggest that you consider implementing a spellcheck function.

Description

• [ ] Source branch in your fork has meaningful name (not main)

Fixes Issue:

Before Merge Checklist

These items can be completed after PR is created.

(Check any items that are not applicable (NA) for this PR)

• [ ] JavaScript implementation
• [ ] Python implementation (NA if HTML beautifier)
• [ ] Added Tests to data file(s)
• [ ] Added command-line option(s) (NA if
• [ ] README.md documents new feature/option(s)

[bitwiseman]

I assume you mean, "turn off the spellcheck function" rather than "implement".

For reference: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/textarea