Update README with project details and image

Added image and updated project description in README.

Author: neilpang

README.md

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 WPF desktop app that captures Windows audio output (any app's playback), streams it to OpenAI's realtime translation model (`gpt-realtime-translate`), and renders the translated audio + dual-language transcript live.
 
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 ## Stack
 
 - **.NET 8** + **WPF** (Windows Desktop)