Update DetectionRuleFile.cs (#1368)

Author: jmikell821

src/Elastic.Markdown/Extensions/DetectionRules/DetectionRuleFile.cs

@@ -50,7 +50,11 @@ private string GetMarkdown()
 		// language=markdown
 		var markdown =
 """
-# Detection Rules Overview
+# Prebuilt detection rules reference
+
+:::{important}
+All prebuilt {{ml}} rules are tagged with `ML`, and their rule type is `machine_learning`. Before using prebuilt {{ml}} rules, ensure you have all of the appropriate requirements.
+:::
 
 """;