Improve README with usage instructions and tech overview

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

README.md

@@ -1 +1,40 @@
 # P2P Poll App
+
+A peer-to-peer polling app where users can add options and vote on them. All data syncs directly between browsers using WebRTC — no central server stores any poll data.
+
+## How It Works
+
+- **Yjs CRDTs** handle shared state — concurrent edits from different peers merge automatically without conflicts
+- **y-webrtc** establishes direct WebRTC connections between browsers (a public signaling server is used only for peer discovery)
+- Each user gets a stable random ID (stored in localStorage) ensuring one vote per user per option
+- Polls are identified by room name, shareable via URL
+
+## Getting Started
+
+```bash
+npm install
+npm run dev
+```
+
+Open `http://localhost:5173` in your browser. To share a specific poll, use the `?room=` query parameter:
+
+```
+http://localhost:5173/?room=my-poll
+```
+
+Share this URL with others to join the same poll.
+
+## Cross-Device Testing
+
+```bash
+npm run dev -- --host
+```
+
+Then open `http://<your-local-ip>:5173/?room=test` on another device on the same network.
+
+## Tech Stack
+
+- [Yjs](https://yjs.dev/) — CRDT library for conflict-free shared state
+- [y-webrtc](https://github.com/yjs/y-webrtc) — WebRTC provider for P2P connectivity
+- [Vite](https://vite.dev/) — Dev server and bundler
+- Vanilla JS — No framework dependencies