docs: add README_SNIPPET.md

Add README snippet for demo and quick start.

Author: HooplaHoorah

README_SNIPPET.md

@@ -0,0 +1,23 @@
+## Demo (2 minutes)
+▶️ https://youtu.be/UONUOS2RKOU
+
+## Screenshots
+<p align="center">
+  <img src="demo/screenshots/01-context-menu.png" width="45%">
+  <img src="demo/screenshots/02-general-dark.png" width="45%"><br/>
+  <img src="demo/screenshots/03-math-dark.png" width="45%">
+  <img src="demo/screenshots/04-general-light.png" width="45%"><br/>
+  <img src="demo/screenshots/05-math-light.png" width="45%">
+</p>
+
+## Quick start
+1. `chrome://extensions` → **Developer mode**
+2. **Load unpacked** → select the `extension/` folder
+3. Highlight text → Right‑click → **Send selection → Web‑to‑Quest**
+
+### AI‑gated features
+- **Summarize / Rewrite** require on‑device Gemini Nano (if available).
+- **Translate / Extract** work everywhere with no network calls.
+
+## Privacy
+General tools process locally. See `PRIVACY.md`.