TKGI-7159 add requirement re: single vCenter

vsphere-nsxt-rpd-mpd.html.md.erb

@@ -55,6 +55,8 @@ Depending on your design choice, <%= vars.k8s_runtime_abbr %> management compone
 
 For each vSphere cluster defined for <%= vars.product_short %>, the following configurations are required to support production workloads:
 
+- All vSphere clusters are managed by the same vCenter server. <%= vars.k8s_runtime_abbr %> does not support workload clusters in multiple vCenter server inventories.
+
 - The vSphere Distributed Resource Scheduler (DRS) is enabled. For more information, see <a href="https://docs.vmware.com/en/VMware-vSphere/6.7/com.vmware.vsphere.resmgmt.doc/GUID-8ACF3502-5314-469F-8CC9-4A9BD5925BC2.html">Creating a DRS Cluster</a> in the vSphere documentation.</p>
 
 - The DRS custom automation level is set to **Partially Automated** or **Fully Automated**. For more information, see <a href="https://docs.vmware.com/en/VMware-vSphere/6.7/com.vmware.vsphere.resmgmt.doc/GUID-C21C0609-923B-46FB-920C-887F00DBCAB9.html">Set a Custom Automation Level for a Virtual Machine</a> in the vSphere documentation.</p>