Update README.md

Update sponsorship link and parameters for getstream.io.

Author: cloudwebrtc

README.md

@@ -11,7 +11,7 @@ WebRTC plugin for Flutter Mobile/Desktop/Web
 <img src="https://stream-blog-v2.imgix.net/blog/wp-content/uploads/f7401112f41742c4e173c30d4f318cb8/stream_logo_white.png?w=350" alt="Stream Chat" style="margin: 8px" />
 </a>
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-Enterprise Grade APIs for Feeds & Chat. <a href="https://getstream.io/chat/flutter/tutorial/?utm_source=https://github.com/flutter-webrtc/flutter-webrtc&utm_medium=github&utm_content=developer&utm_term=flutter" target="_blank">Try the Flutter Chat tutorial</a> 💬
+Enterprise Grade APIs for Feeds, Chat, & Video. <a href="https://getstream.io/video/docs/flutter/?utm_source=https://github.com/flutter-webrtc/flutter-webrtc&utm_medium=sponsorship&utm_content=&utm_campaign=webrtcFlutterRepo_July2023_video_klmh22" target="_blank">Try the Flutter Video tutorial</a> 💬
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