Add README with demo GIF

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

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 crt
 nimcache/
-demo.gif
 demo.png/

README.md

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+# terminal-oscilloscope
+
+A terminal-based oscilloscope with CRT phosphor physics, written in Nim using [illwill](https://github.com/johnnovak/illwill).
+
+![demo](demo.gif)
+
+## Features
+
+- **CRT boot/shutdown animations** — phosphor ramp, beam sweep, vertical collapse, dot fade
+- **Y-T and X-Y modes** — time-domain waveform or Lissajous figures
+- **Phosphor persistence** — beam bloom, decay trails, intensity-based shading
+- **Half-block rendering** — 2x vertical resolution using Unicode `▀▄█` characters
+- **Live audio capture** — visualises system audio via ffmpeg/PulseAudio monitor
+- **Demo mode** — built-in synthesised waveforms when no audio source is available
+
+## Install
+
+Requires [Nim](https://nim-lang.org/) 2.x.
+
+```bash
+git clone https://github.com/rolandnsharp/terminal-oscilloscope.git
+cd terminal-oscilloscope
+nimble build
+./crt
+```
+
+## Controls
+
+| Key | Action |
+|-----|--------|
+| `m` | Toggle Y-T / X-Y mode |
+| `+` / `-` | Increase / decrease gain (amplitude) |
+| `]` / `[` | Zoom in / out time axis |
+| `g` | Cycle grid: full → crosshair → off |
+| `space` | Freeze display |
+| `d` | Cycle demo frequency presets |
+| `q` | Quit (with CRT shutdown effect) |
+
+## Audio
+
+Captures system audio automatically using `ffmpeg` with the PulseAudio/PipeWire monitor of your default output sink. Falls back to `parec` if available, or a built-in demo signal.
+
+No extra packages needed — just `ffmpeg` (pre-installed on most Linux systems).
+
+## Credits
+
+CRT turn-on/off animations inspired by [AetherTune](https://github.com/nevermore23274/AetherTune).