Update README to reflect SDK usage and development workflow

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

Author: underthestars-zhy

README.md

@@ -1,15 +1,47 @@
 # @photon-ai/whatsapp-business
 
-To install dependencies:
+TypeScript SDK for the WhatsApp Business API via Photon's Spectrum gRPC gateway.
+
+## Installation
 
 ```bash
-bun install
+bun add @photon-ai/whatsapp-business
 ```
 
-To run:
+## Quick start
 
-```bash
-bun run src/index.ts
+```ts
+import { createClient } from "@photon-ai/whatsapp-business";
+
+const client = createClient({
+  accessToken: process.env.WA_ACCESS_TOKEN!,
+  phoneNumberId: process.env.WA_PHONE_NUMBER_ID!,
+  appSecret: process.env.WA_APP_SECRET!,
+});
+
+// Send a text message
+await client.messages.send({
+  to: "+1234567890",
+  text: { body: "Hello from the SDK!" },
+});
+
+// Subscribe to inbound events
+const stream = client.events.subscribe();
+for await (const event of stream) {
+  console.log(event);
+}
+
+await client.close();
 ```
 
-This project was created using `bun init` in bun v1.3.5. [Bun](https://bun.com) is a fast all-in-one JavaScript runtime.
+## Development
+
+```bash
+bun install          # install dependencies
+bun run generate     # regenerate protobuf types
+bun run build        # generate + bundle with tsup
+bun run check        # type-check
+bun run lint         # lint with Biome
+bun run lint:fix     # auto-fix lint issues
+bun test             # run tests
+```