Document defaultProps in README

[scott-ln]

defaultProps are not mentioned at all in the README. This is not useful if you've just gotten an error from eslint-plugin-react/require-default-props. The top Google hit for "React defaultProps" is this page on the React site which directs you to look at the prop-types documentation instead.

[ljharb]

A sentence that points back to https://reactjs.org/docs/typechecking-with-proptypes.html#default-prop-values seems reasonable.

[scott-ln]

Just looked at that page again and I see now that the message at the top which I mentioned is intended for people who were using the old React.PropTypes. That wasn't clear to me as a new user encountering an important-looking yellow box at the start of the page, so perhaps it could be moved a little further down the page.

[ljharb]

I have no control over react’s docs; you’d have to file an issue/PR on react itself for that.

[scott-ln]

Gotcha, will do - thanks Jordan.

[ljharb]

Closing in favor of reactjs/react.dev#3632