[Docs] Write theme setup and usage guide

[hta218]

Context

Naturélle needs clear setup and usage docs so developers, interns, and merchants can run/customize it without tribal knowledge.

Goal

Write a Naturélle setup and usage guide covering local development, Shopify/Weaverse connection, and production deployment.

Scope

Document:

• Project overview and intended use case
• Prerequisites
• Install and local development steps
• Required env vars with placeholder values only
• How to connect to Shopify Hydrogen/storefront API
• How to connect/use Weaverse Studio
• How to customize theme settings
• How to deploy to Oxygen/production
• Common troubleshooting issues

Security requirements:

• Do not include real secrets or tokens.
• Clearly distinguish public storefront keys from private/admin tokens.
• Explain local .env vs production/Oxygen environment variable setup.

Deliverables

• Updated README.md and/or docs/setup.md
• Env var table with placeholder examples
• Troubleshooting section

Acceptance criteria

• A new developer can run Naturélle locally from the docs.
• Env vars are documented safely with placeholders.
• Local vs production env setup is clear.
• Weaverse Studio connection is explained.
• Deployment notes are included.

Metadata

• Theme: Naturélle
• Track: Theme Refresh
• Priority: High
• Milestone: July-2026