Document how to get Genability credentials

[jpvelez]

What

Add a section to the docs that explains how to get Genability credentials, or at least links to such instructions. Then link to it when we say "Cannot use Genability due to missing credentials"

Why

I'm running the tool without setting up the Genability credentials first, and it's asking for them. But that begs the question: where do I get these credentials? Every user is going to have to figure this out, so we should help usability and tell them.

Deliverables

• New section of the docs that either documents where to get credentials, or links to such docs
• A link to our docs in the cli tool message that says "credentials missing"

[linear]

TOO-6

[MeadBarrel]

Updated the documentation https://switchbox-data.github.io/tariff_fetch/providers/arcadia/access/