Link to @visgl/react-google-maps from README

[wangela]

Now that https://goo.gle/react-google-maps is stable, people who end up here may be interested in the full React support offered by that library beyond the loading wrapper that this library offers.

Let's add a link to the React Google Maps Library (both the homepage and the npm page) from the README of this library.

[jalvaradoas39]

I'd love to take this on! If it's okay with you, @wangela, I'd be happy to add the links to the README. Let me know if I should proceed, and I'll get started.