add a README.md with basics, and target pnpm instead of npm

README.md

@@ -0,0 +1,34 @@
+A lightweight Express service that schedules and sends Firebase Cloud Messaging (FCM) push notifications to wake up registered devices.
+
+## Dev
+
+```bash
+cp .env.example .env
+```
+
+Edit .env — set FIREBASE_SERVICE_ACCOUNT_JSON
+Here is one way to generate the contents: `cat your-downloaded-key.json | jq -c .`
+
+```bash
+pnpm install
+pnpm run dev
+```
+
+The server starts on `http://localhost:3000` (or the port in `PORT`). Hot-reloads on file changes.
+
+Set `NODE_ENV=test-local` in `.env` to bypass JWT expiry verification during local development.
+
+## Production
+
+```bash
+pnpm install --omit=dev
+pnpm start
+```
+
+Required environment variables:
+
+| Variable | Description |
+|---|---|
+| `FIREBASE_SERVICE_ACCOUNT_JSON` | Inline service account JSON (one line). If unset, falls back to Application Default Credentials. |
+| `PORT` | HTTP port (default: `3000`). |
+| `FCM_TOKEN_DATA_DIR` | Directory for persisting registered FCM tokens (default: `./data`). |