Update README to clarify 'users:read' scope

Clarified the purpose of the 'users:read' scope in the README.

Author: danishi

README.md

@@ -82,7 +82,7 @@ The Agent Development Kit includes a built-in web-based Development UI that you
    - `mpim:history`
    - `files:read`
    - `reactions:write`
-   - `users:read` — used to resolve user display names for speaker identification in threads
+   - `users:read`
 3. Install the app to your workspace to obtain `SLACK_BOT_TOKEN` and `SLACK_SIGNING_SECRET`.
 4. Enable **Event Subscriptions** and set the Request URL to `https://<your-cloud-run-service-url>/slack/events`.
 5. Subscribe to bot events: `app_mention`.