docs: add README.md with project overview and usage instructions

Co-authored-by: aider (gemini/gemini-3.1-pro-preview) <aider@aider.chat>

README.md

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+# Headless Audio Player
+
+A lightweight, headless Python audio player designed as a fast drop-in replacement for `mpv`. 
+
+## What it does
+- Decodes and resamples common audio formats to `48000Hz`, `stereo`, `s16` PCM.
+- Applies on-the-fly EBU R128 volume normalization using FFmpeg's `loudnorm` filter.
+- Outputs raw PCM audio directly to a FIFO pipe (`/tmp/snapfifo`).
+- Provides a JSON IPC server over a Unix socket for real-time playback control (pause, volume, seek, quit).
+
+## What it's for
+This player is specifically built to act as a backend player for music servers like **Navidrome** (in Jukebox mode) feeding into multi-room audio systems like **Snapcast**. It avoids the overhead of full `mpv` while maintaining compatibility with its IPC protocol.
+
+## How to use it
+
+1. Install the required dependencies (Python 3.11+ recommended):
+   ```bash
+   pip install av numpy
+   ```
+
+2. Run the player, specifying the IPC socket path and the audio file:
+   ```bash
+   python main.py --input-ipc-server=/tmp/mpv-socket /path/to/song.flac
+   ```