Link to the docs that describe the config file are broken

[Gibbsdavidl]

On the readme, there's a link that should take us to a page that describes the config.yml structure and options, but it's broken and I think that's it for documentation on this.

From the readme: A description of what the various keys in this file represent can be found in the Fill in Configuration File(s) section of the schematic docs.

[adamjtaylor]

Thanks @Gibbsdavidl for spotting this dead link to old external documentation.

I will make a simple edit to point towards the docs on the schematicpy.

@aditigopalan lets talk on Friday about updating the readme here in any case to align with best practices from other Sage data model repos