Update New-OrganizationRelationship.md

Adds guidance for max group size in FreeBusyAccessScope.

Author: alexcotsalas

exchange/exchange-ps/ExchangePowerShell/New-OrganizationRelationship.md

@@ -284,7 +284,7 @@ Accept wildcard characters: False
 
 > Applicable: Exchange Server 2010, Exchange Server 2013, Exchange Server 2016, Exchange Server 2019, Exchange Online, Exchange Online Protection
 
-The FreeBusyAccessScope parameter specifies a mail-enabled security group in the internal organization that contains users whose free/busy information is accessible by an external organization. You can use any value that uniquely identifies the group. For example:
+The FreeBusyAccessScope parameter specifies a mail-enabled security group in the internal organization that contains users whose free/busy information is accessible by an external organization. For best performance, groups should be smaller than 10,000 members. You can use any value that uniquely identifies the group. For example:
 
 - Name
 - Distinguished name (DN)