Docs: Update 7.4 What's New to use more correct description of alerting…

Docs: Update 7.4 What's New to use more correct description of alerting notification template feature (#30502)

* use more correct description of feature

* reference variable templating

* add word

docs/sources/whatsnew/whats-new-in-v7-4.md

@@ -83,9 +83,9 @@ The main use case is for [multi-dimensional](https://grafana.com/docs/grafana/la
 
 > **Note:** Queries built with this feature might break with minor version upgrades until Grafana 8 is released. This feature does not work with the current Grafana alerting.
 
-### Variable support in alert notifications
+### Alert notification query label interpolation
 
-You can now provide detailed information to alert notification recipients by injecting alert query data into an alert notification. Labels that exist from the evaluation of the alert query can be used in the alert rule name and in the alert notification message fields. The alert label data is injected into the notification fields when the alert is in the alerting state. When there are multiple unique values for the same label, the values are comma-separated.
+You can now provide detailed information to alert notification recipients by injecting alert label data as template variables into an alert notification. Labels that exist from the evaluation of the alert query can be used in the alert rule name and in the alert notification message fields using the `${Label}` syntax. The alert label data is automatically injected into the notification fields when the alert is in the alerting state. When there are multiple unique values for the same label, the values are comma-separated.
 
 {{< figure src="/img/docs/alerting/alert-notification-template-7-4.png" max-width="700px" caption="Variable support in alert notifications" >}}