Doc Hackathon: Issue#1465 #1465 (#2924)

Added a note saying that the version of Docker CS Engine must be the same for all nodes. #1465

Author: constanzekratel

datacenter/ucp/2.1/guides/admin/install/index.md

@@ -10,7 +10,7 @@ installed on-premise or on a cloud infrastructure.
 ## Step 1: Validate the system requirements
 
 The first step to installing UCP, is ensuring your
-infrastructure has all the [requirements UCP needs to run](system-requirements.md).
+infrastructure has all the [requirements UCP needs to run](system-requirements.md). You also need to ensure that all nodes (physical or virtual) are running the same version of CS Docker Engine.
 
 
 ## Step 2: Install CS Docker on all nodes