Update metric-alert-config.mdx (#9156)

Add note archived issues are excluded.

Author: vivianyentran

docs/product/alerts/create-alerts/metric-alert-config.mdx

@@ -10,6 +10,10 @@ Sentry provides several configuration options to create a metric alert based on
 
 To create a metric alert you first need to choose a metric type. For some alert types the function is built into the alert and for others you can choose functions and parameters to apply to it. For example, if you select “Users Experiencing Errors”, that translates to the function, `count_unique(user.id)`. Since editing this function would change the nature of the alert, it is not editable and thus hidden. On the other hand, if you select “Largest Contentful Paint” the measurement used is `measurement.lcp`, you also need to choose a function, e.g. `p75()`, for a combined metric function of `p75(measurement.lcp)`.
 
+<Note>
+By default, metric alerts exclude archived issues. For instance, an alert for "Number of Errors" does not count errors from archived issues. If you want your metric alerts include archived issues, you can manually add `is:archived` to your [filters](#filters).
+</Note>
+
 ### Metrics Types for Alerting
 
 #### Errors