integrations: Update documentation for Grafana Integration.

The process for creating an integration has changed since
Grafana 8.3.

zerver/webhooks/grafana/doc.md

@@ -4,6 +4,29 @@ See your Grafana dashboard alerts in Zulip!
 
 1. {!create-bot-construct-url.md!}
 
+### Instructions for Grafana 8.3 and above
+
+1. In Grafana, go to **Alerting**. Click on **Contact points**, and
+   then **Add contact point**.  Configure the new contact point as
+   follows: set the name; under **Integration** choose Webhook, and
+   set **URL** to the URL constructed above; under **Optional Webhook
+   settings** choose **POST** as the **HTTP method**.  Click on
+   **Test** to send a test notification and if all is good, click on
+   **Save contact point**.
+1. Under **Notification policies** create a new policy (for example, a
+   **New nested policy** of the **Default policy**), setting the
+   **Matching label** as **Zulip** = 1, and selecting the **Contact
+   point** as the one created in the step above. Click on **Save
+   policy**.
+1. Under **Alert rules**, click on **Create alert rule**, where you
+   will specify the conditions to fire the alert. Make sure you set
+   the **Rule name**, and in the **Notifications** section add a label
+   that matches the label created in the step above. Customize the
+   **query and alert condition**, **alert evaluation behavior**, etc.
+   and click on **Save rule**.
+
+### Instructions for Grafana 8.2 and below
+
 1. In Grafana, go to **Alerting**. Click on **Notification channels**.
    Configure **Edit Notification Channel** as appropriate for your
    alert notification. Set the name. Under **Type**, choose **webhook**.