Create quickstart.md

[milcastob]

Added a tiny quickstart that explains what to export and how to run a basic stream locally.

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Note

Introduces a concise local quickstart to help run the app end-to-end.

• Adds docs/quickstart.md with npm install, environment variables (WS_URL, API_KEY), run steps (npm run build, npm run start), and basic troubleshooting guidance

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