Added clarification for unregistered cores re the execution time

Author: anosov1960

samples/manage/azure-hybrid-benefit/README.md

@@ -42,7 +42,7 @@ The following resources are in scope for the license utilization analysis:
 > - For PaaS workloads, each vCore of Business Critical service tier is counted as one Enterprise vCore and each vCore of General Purpose service tier is counted as one Standard vCore.
 > - In the DTU-based purchasing model, the SQL license cost is built into the individual SKU prices. These resources are not eligible for Azure Hybrid Benefit or HADR benefit, and therefore are not in scope of the tool.
 > - You must be at least a *Reader* of each subscription you scan. 
-> - To report unregistered vCores, you must be a subscription *Contributor* or *Owner*, otherwise this column will show a zero value.
+> - To report unregistered vCores, you must be a subscription *Contributor* or *Owner*, otherwise this column will show a zero value. Selecting this option will substantially increase the execution time, especially for the   subscriptions with large numbers of virtual machines.
 > - The values AHB ECs and PAYG ECs are reserved for the future use and should be ignored
 
 # Launching the script