Added a note to differentiate legacy and new alerts. (#35385) (#35387)

(cherry picked from commit ec9b9d6ab1)

Co-authored-by: achatterjee-grafana <70489351+achatterjee-grafana@users.noreply.github.com>

docs/sources/alerting/old-alerting/_index.md

@@ -6,7 +6,9 @@ weight = 114
 
 # Legacy Grafana alerts
 
-Legacy Grafana alerts consists of two parts:
+Grafana 8.0 has [new and improved alerts]({{< relref "../unified-alerting/_index.md" >}}). The new alerting system are an opt-in feature that centralizes alerting information for Grafana managed alerts and alerts from Prometheus-compatible data sources in one UI and API.
+
+Out of the box, Grafana still supports legacy dashboard alerts. Legacy Grafana alerts consists of two parts:
 
 Alert rules - When the alert is triggered. Alert rules are defined by one or more conditions that are regularly evaluated by Grafana.
 Notification channel - How the alert is delivered. When the conditions of an alert rule are met, the Grafana notifies the channels configured for that alert.

docs/sources/alerting/unified-alerting/_index.md

@@ -7,7 +7,7 @@ weight = 113
 # Overview of Grafana 8 alerts
 Alerts allow you to know about problems in your systems moments after they occur. Robust and actionable alerts help you identify and resolve issues quickly, minimizing disruption to your services.
 
->**Note:** This information is for the new, Grafana 8 Alerts. This is an [opt-in]({{< relref"./opt-in.md" >}}) feature released in Grafana 8.0. Grafana still supports [dashboard alerts]({{< relref "../old-alerting/_index.md" >}}) out of the box
+>**Note:** This information is for the new, Grafana 8 Alerts. This is an [opt-in]({{< relref"./opt-in.md" >}}) feature released in Grafana 8.0. Grafana still supports [legacy dashboard alerts]({{< relref "../old-alerting/_index.md" >}}) out of the box
 
 Alerts have four main components: