added section on multihost requirements

Author: bfallonf

install_config/install/prerequisites.adoc

@@ -115,8 +115,8 @@ Storage in Red Hat Enterprise Linux Atomic Host] for instructions on configuring
 this during or after installation.
 ====
 
-[[sizing-recommendations]]
-=== Sizing Recommendations
+[[host-recommendations]]
+=== Host Recommendations
 The following apply to production environments. Test or sample environments will
 function with the minimum requirements.
 
@@ -129,6 +129,9 @@ above, for each 1000 pods. Therefore, the recommended size of master host in an
 well as the minimum requirements for a master host of 2 CPU cores and 8 GB of
 RAM.
 
+When planning an environment with multiple masters, a minimum of three etcd
+hosts as well as a load-balancer between the master hosts, is required.
+
 *Node Hosts*
 
 The size of a node host depends on the expected size of its workload. As an