Put all cluster docs in the right documentation group

Summary: Some of these had the wrong `@group` header.

Test Plan: `grep`

Reviewers: chad

Reviewed By: chad

Differential Revision: https://secure.phabricator.com/D15778

src/docs/user/cluster/cluster_daemons.diviner

@@ -1,5 +1,5 @@
 @title Cluster: Daemons
-@group intro
+@group cluster
 
 Configuring Phabricator to use multiple daemon hosts.
 

src/docs/user/cluster/cluster_databases.diviner

@@ -1,5 +1,5 @@
 @title Cluster: Databases
-@group intro
+@group cluster
 
 Configuring Phabricator to use multiple database hosts.
 

src/docs/user/cluster/cluster_notifications.diviner

@@ -1,5 +1,5 @@
 @title Cluster: Notifications
-@group intro
+@group cluster
 
 Configuring Phabricator to use multiple notification servers.
 

src/docs/user/cluster/cluster_repositories.diviner

@@ -1,5 +1,5 @@
 @title Cluster: Repositories
-@group intro
+@group cluster
 
 Configuring Phabricator to use multiple repository hosts.
 

src/docs/user/cluster/cluster_webservers.diviner

@@ -1,5 +1,5 @@
 @title Cluster: Web Servers
-@group intro
+@group cluster
 
 Configuring Phabricator to use multiple web servers.