feat: Write integrator documentation

[lornakelly]

Description

Write integrator documentation covering how to install the npm package, embed the editor component, and provide workflow content to it. This should give consumers enough guidance to get started with setup and usage.

Motivation

Make it easier for integrators to adopt the editor by providing clear guidance on installation and implementation.

Proposed Implementation

No response

Definition of Done

• Implementation: Fully implemented according to the Serverless Workflow spec.
• Unit Tests: Comprehensive unit tests are included and passing.
• Integration Tests: Verified within the monorepo and target environments (Web/VS Code).
• Documentation: Updated README.md, ADRs, or official docs.
• Performance: No significant regression in editor responsiveness.
• Accessibility: UI changes comply with accessibility standards.