Added comprehensive system dependencies section for Debian/Ubuntu:

Required system packages:
- build-essential, cmake, pkg-config (build tools)
- ffmpeg (video processing)
- libavformat-dev, libavcodec-dev, libavdevice-dev, libavutil-dev
- libavfilter-dev, libswscale-dev, libswresample-dev (FFmpeg dev libs)
- libsdl2-dev, libssl-dev, libcurl4-openssl-dev
- python3-dev

These are required for:
- PyAV (av package) - needed by audiocraft/MusicGen
- face-recognition (dlib)
- Building Python extensions

Updated quick install instructions to include system dependencies step.