fix options usage example in readme

[gschurck]

Thanks for this useful project !

I saw there is an issue in the readme.
When we do

const options = {
  src: 'https://storage.googleapis.com/gtv-videos-bucket/sample/ElephantsDream.mp4',
};
const videoEditor = new VideoEditor({ options });

The options are not passed to the VideoEditor.

We need to use

const videoEditor = new VideoEditor(options);

[aslamhus]

Thank you for spotting this!