Docs: Mention that the eslint plugin uses checkSync due to an ESLint limitation

[thernstig]

What is the problem?

It would be nice if https://makenowjust-labs.github.io/recheck/docs/usage/as-eslint-plugin/ mentions that the ESLint plugin uses checkSync due to a limitation in ESLint. And possibly also link to the issue in ESLint so people are aware what the limitation is.

I am fine with this being closed directly if not wanted as it is an implementation detail, but it might be nice for users wondering. Maybe even more important if this package becomes the default in eslint-community/eslint-plugin-security#28.

[makenowjust]

Please make a pull request and I will merge it.

[thernstig]

@makenowjust I have not got the time right now, but maybe in the future.