Document Modal publication

[WillEngler]

There should be a page where we can send someone who wants to publish a garden using Modal. It should instruct them on how to set up a Modal account, make their app, submit it to Garden, and execute it.

Assumptions:

Acceptance Criteria

Given I am a collaborator to the Garden project, when I want to get started with Modal, then there is a handy page the Garden dev team can point me to.