Update index.yml

Author: msmbaldwin

articles/security/benchmarks/index.yml

@@ -9,6 +9,7 @@ metadata:
   services: security
   ms.service: security
   ms.subservice: fundamentals
+  ms.custom: security-baselines
   ms.topic: landing-page
   author: msmbaldwin
   ms.author: mbaldwin
@@ -55,4 +56,4 @@ landingContent:
           - text: Shared responsibility in the cloud
             url: ../fundamentals/shared-responsibility.md
           - text: Azure Security Center
-            url: ../../security-center/index.yml
+            url: ../../security-center/index.yml