Create docs for setting up a store

[gabeabrams]

Create a file: docs/SET_UP.md

• Store metadata and structure
• Catalog metadata and structure
• App metadata and structure (screenshots, guides, icons, metadata, credentials)
  ^ specifically explain message before/after install and uninstall, explain request emails and that admins can bypass that
• Inheritance and extending apps
• Assigning account ids to catalogs
• Explain hot reloading and how if you want to make changes and have them not go live, use beingEdited in the store metadata