Update Set-CsTenantFederationConfiguration.md

AllowedTrialTenantDomains parameters docs improved.

Author: rhrivnak

teams/teams-ps/teams/Set-CsTenantFederationConfiguration.md

@@ -513,8 +513,13 @@ Accept wildcard characters: False
 ```
 
 ### -AllowedTrialTenantDomains
-You can provide list of trial tenant domains which are excluded from blocking when `ExternalAccessWithTrialTenants` is set to `Blocked`.
-This allows you to have trial tenant block enabled but still selectively allow communication with some trial tenants.
+You can whitelist specific "trial-only" tenant domains, while keeping the `ExternalAccessWithTrialTenants` set to `Blocked`. This will allow you to protect your organization against majority of tenants that don't have any paid subscriptions, while still being able to collaborate externally with those trusted trial-tenants in the list. 
+ 
+Note: 
+- the list supports up to maximum 4k domains.
+- if `ExternalAccessWithTrialTenants` is `Allowed`, then the contents of the `AllowedTrialTenantDomains` list will be ignored.
+- if a domain in the list belongs to a "Trial-Only" tenant will be validated by the system during setting enforcement. If it's not, then that domain will be ignored.
+- the domains in the list need to be added explicitly. For example, if `contoso.com` is allowed, then `sales.contoso.com` will still get blocked unless it is added explicitly to the list.
 
 ```yaml
 Type: List