Add a README generation workflow for package documentation

[coderabbitai]

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Summary

Create a reusable README generation workflow for package documentation so example snippets and shared sections can stay in sync with source examples and templates.

Rationale

During review of #466, we discussed that keeping a small quick start in packages/js/README.md is helpful, but longer term it would be better to reduce duplication and maintenance drift. A generator or template-based approach was proposed as a follow-up so README content can be derived from a single source of truth.

By copying the code from example apps, we can also guarantee that the code runs properly.

Requested changes

• Design a README generation approach for package documentation, such as:
  • a README.template.md workflow, and/or
  • generated sections sourced from example app files or structured data.
• Identify which sections should remain hand-written versus generated.
• Ensure code examples can be pulled from real example sources where practical.
• Document how the generation step should be run and maintained.
• Preserve npm-friendly rendering for generated output.

Affected areas

• packages/js/README.md
• Example application sources used for embedded snippets
• Any script(s) or template(s) introduced for README generation
• Documentation workflow for package publishing

Acceptance criteria

• There is a documented generation strategy for package README content.
• At least one generated section is sourced from a canonical example or template.
• The resulting README remains suitable for npm and GitHub rendering.
• The workflow reduces duplication without making simple README edits unnecessarily difficult.

Backlinks

• Source PR: docs(packages/js): add README for npm package #466
• PR URL: docs(packages/js): add README for npm package #466
• Discussion comment: docs(packages/js): add README for npm package #466 (comment)

Requested by: @Ryan-Millard