docs(readiness): list a company new to sourcey in the same pull request

[auscaster]

A listing pull request can now name a company Sourcey does not list yet, by adding a company block (summary and site URL) next to entity and a fresh entity_id.

This documents that path:

• Choose a path and Before you edit no longer send a new company to a listing request first.
• A new A company new to Sourcey section covers the company block, a command that generates a valid entity_id, how the company is listed (free under the automatic listing rule, otherwise a US$29 verification by a person, linked from the check), and that the check runs again by itself once the company is live.
• It also states the limits: one new company per pull request, with authority_intent: community and offer_relations: [].

Documentation only; no listing or workflow file changes.

[sourcey]

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Sourcey can't admit this change automatically, so a maintainer reviews it. You don't need to do anything.

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! A maintainer reviews this change.

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[sourcey]

A maintainer will review your pull request

Sourcey can't admit this change automatically, so a maintainer reviews it. You don't need to do anything.

Follow your pull request on Sourcey

! A maintainer reviews this change.

• The pull request changes more than the repository's data or one declared pin.

[sourcey]

A maintainer will review your pull request

Sourcey can't admit this change automatically, so a maintainer reviews it. You don't need to do anything.

Follow your pull request on Sourcey

! A maintainer reviews this change.

• The pull request changes more than the repository's data or one declared pin.

[auscaster]

Folded into #394, which carries this change with the other CONTRIBUTING updates so they land in one review.