docs: add bilingual (EN & ZH) docs and examples for parallel flow usage

[lucky-peak]

Summary

Related Issue(s)

• Closes #123
• Fixes #456

Changes

• Feature A added

contents

• Refactor B

contents

• Fix for C

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Screenshots (if UI changes)

Checklist

• been self-reviewed.
  • Code is formatted
  • Tests added/updated
  • All CI checks passed
  • Documentation updated
• added documentation for new or modified features or behaviors.
• added new features, such as new agents, new flows, etc.
• added or updated version, license, or notice information.
• added or updated demo, integration tests, unit tests, or others.
• added or updated ui, or had changes in frontend.