Notify a Slack #channel when you join a room.

Setup

1. Create a Slack app at https://api.slack.com/apps — click Create New App → From scratch, name it (e.g. "Tuple Room Notify"), and pick the workspace you want to post to.
2. In the app's sidebar, open Incoming Webhooks and toggle it on.
3. Click Add New Webhook to Workspace, choose the channel that should receive notifications, and click Allow.
4. Copy the webhook URL that Slack generates.

In the room-joined script, replace the SLACK_WEBHOOK_URL value with your webhook URL.