Move performance section under "Digging Deeper" [ci-skip]

This section was moved to "Advanced Active Record" in
35ad43b by accident.

Author: p8

guides/source/documents.yaml

@@ -234,6 +234,10 @@
       name: Using Rails for API-only Applications
       url: api_app.html
       description: This guide explains how to effectively use Rails to develop a JSON API application.
+    -
+      name: Tuning Performance for Deployment
+      url: tuning_performance_for_deployment.html
+      description: This guide covers performance and concurrency configuration for deploying your production Ruby on Rails application.
 
 -
   name: Advanced Active Record
@@ -256,10 +260,6 @@
       name: Composite Primary Keys
       url: active_record_composite_primary_keys.html
       description: This guide is an introduction to composite primary keys for database tables.
-    -
-      name: Tuning Performance for Deployment
-      url: tuning_performance_for_deployment.html
-      description: This guide covers performance and concurrency configuration for deploying your production Ruby on Rails application.
 
 -
   name: Extending Rails