Add clarification notice about Flow/React support to the readme

[kripod]

In the readme’s “Recommended Configuration” section, there are no instructions about the need to add e.g. ”extends”: [”prettier/react”] to support its corresponding ESLint plugin.

I think there should be at least a clarification notice about this for disabling rules of special ESLint plugins (e.g. eslint-plugin-react).

Example: https://github.com/kripod/gatsby-starter-modern/blob/cabc047185ffdfe27c29d31071999d80fe39b474/.eslintrc.json#L3

[not-an-aardvark]

Sounds reasonable to me, would you be interested in creating a PR?

[kripod]

Sure, it’s done.