Add metadata information to the customize chunk documentation

[Liquid-Blocks]

The customize chunk doc should also explain how to use the metadata directly (allowing pros to use the cli).

The metadata should be in the following format for the backend to update the chunk:

{
    “77223001”: {
        chunks: [<chunkID>],
        name: <string>,
        logo: <url>,
        image: <url>,
        portal: <url>,
        planet: <url>
    }
}