added demo video to the README

Author: trudypainter

README.md

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 This repository contains a react-based starter app for using the [Multimodal Live API]([https://ai.google.dev/gemini-api](https://ai.google.dev/api/multimodal-live)) over a websocket. It provides modules for streaming audio playback, recording user media such as from a microphone, webcam or screen capture as well as a unified log view to aid in development of your application.
 
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+[![Multimodal Live API Demo](readme/thumbnail.png)](https://www.youtube.com/watch?v=J_q7JY1XxFE)
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+Watch the demo of the Multimodal Live API [here](https://www.youtube.com/watch?v=J_q7JY1XxFE).
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+---
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 To get started, [create a free Gemini API key](https://aistudio.google.com/apikey). We have provided several example applications on other branches of this repository:
 
 - [demos/GenExplainer](https://github.com/google-gemini/multimodal-live-api-web-console/tree/demos/genexplainer)