[Reference] Revisit Security landing page (#1304)

This PR updates the Security landing page.
Relates to #1303

## Notes for the reviewers

I'm not sure what the correct link would be for [Detection Rules
Overview](//detection-rules/docs/index.md). This page is a collection of
links.

---------

Co-authored-by: Nastasha Solomon <[email protected]>

Author: alaudazzi

reference/security/index.md

@@ -7,13 +7,11 @@ applies_to:
 
 # Security
 
-This section of the documentation contains reference information for [{{elastic-sec}}](/solutions/security.md) features, including:
+This section contains reference information for {{elastic-sec}} features, including:
 
-* Prebuilt rules
-* Downloadable rule updates
-* Prebuilt jobs
-* Fields and object schemas
-* Endpoint command reference
-* Prebuilt anomaly detection jobs
+* [Fields and object schemas](/reference/security/fields-and-object-schemas/index.md)
+* [Endpoint command reference](/reference/security/endpoint-command-reference.md)
+* [Detection Rules Overview](detection-rules://index.md)
 
-You can use [APIs](/solutions/security/apis.md) to interface with {{elastic-sec}} features.
+To learn more about Security features and how to get started, refer to [{{elastic-sec}}](/solutions/security.md).
+To interface with {{elastic-sec}} features, you can use these [APIs](/solutions/security/apis.md).