Improves screenshots on overview docs

overview.md

@@ -15,7 +15,7 @@ Docker Universal Control Plane (UCP) is the enterprise-grade cluster management
 solution from Docker. You install it behind your firewall, and it helps you
 manage your whole cluster from a single place.
 
-![](images/replica-nodes.png)
+![](images/overview-1.png)
 
 ## Centralized cluster management
 
@@ -23,7 +23,7 @@ Docker UCP can be installed on-premises, or on a virtual private cloud.
 And with it, you can manage thousands of nodes as if they were a single one.
 You can monitor and manage your cluster using a graphical UI.
 
-![](images/container-detail-2.png)
+![](images/overview-2.png)
 
 Since UCP exposes the standard Docker API, you can continue using the tools
 you already know, to manage a whole cluster.
@@ -60,6 +60,8 @@ Docker UCP has its own built-in authentication mechanism, and supports LDAP
 and Active Directory. It also supports Role Based Access Control (RBAC).
 This ensures that only authorized users can access and make changes to cluster.
 
+![](images/overview-3.png)
+
 Docker UCP also integrates with Docker Trusted Registry and Docker Content
 Trust. This allows you to keep your images stored behind your firewall,
 where they are safe. It also allows you to sign those images to ensure that