First draft (#7013)

Author: nastasha-solomon

docs/detections/building-block-rule.asciidoc

@@ -10,6 +10,8 @@ in the UI. This is useful when you want:
 You can then use building block rules to create hidden alerts that act as a
 basis for an 'ordinary' rule to generate visible alerts.
 
+TIP: Add <<rule-notifications, rule notifications>> to building block rules to notify you when building block alerts are generated. 
+
 [float]
 === Set up rules that run on alert indices