Improve description for NotificationMode

Author: get-itips

skype/skype-ps/skype/New-CsTeamsEmergencyCallingPolicy.md

@@ -156,6 +156,7 @@ Accept wildcard characters: False
 
 ### -NotificationMode
 The type of conference experience for security desk notification.
+Possible values are NotificationOnly, ConferenceMuted, ConferenceUnMuted.
 
 ```yaml
 Type: Microsoft.Teams.Policy.Administration.Cmdlets.Core.NotificationMode