docs: added heatmap layer example

[barakplasma]

see the issue for adding examples

fixes issue #561

I'm getting an error, which is why this is still a draft:

Invariant Violation: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: object.

I think it's connected to the import, but I don't have time to figure out why it isn't working right now.

[JustFly1984]

@barakplasma The repo of this project is unmaintained more than a year, and we had build new version https://www.npmjs.com/package/@react-google-maps/api

We had rewrite it to TypeScript, and updating it frequently: https://github.com/JustFly1984/react-google-maps-api/tree/master/packages/react-google-maps-api You can enjoy autocomplete.

You can see our docs: https://react-google-maps-api-docs.netlify.com/

Also a lot of examples: https://react-google-maps-api-gatsby-demo.netlify.com/ https://github.com/JustFly1984/react-google-maps-api/tree/master/packages/react-google-maps-api-gatsby-example/src/examples

The bundle size is much smaller: https://bundlephobia.com/result?p=@react-google-maps/[email protected]

Enjoy!