add sentence for utility matchers

Author: lobsterkatie

docs/concepts/data-management/event-grouping/fingerprint-rules.mdx

@@ -148,6 +148,8 @@ Used to "scope" down the matcher. The following families exist: `javascript` for
 family:native !stack.module:"myproject::*" -> not-from-my-project
 ```
 
+Additionally, the folowing utility matchers are available:
+
 ### `app`
 
 Checks if the frame is in-app or not. It is particularly useful when combined with another matcher. Possible values are `yes` and `no`: