doc fix for get-azadgroupmember (Azure#16744)

Author: VeryEarly

src/Resources/Resources/help/Get-AzADGroupMember.md

@@ -8,7 +8,7 @@ schema: 2.0.0
 # Get-AzADGroupMember
 
 ## SYNOPSIS
-Lists members from group.
+Lists members from group. Currently service principals are not listed as group members due to staged roll-out of service principals on Graph V1.0 endpoint. Please see [documentation of the REST API](https://docs.microsoft.com/en-us/graph/api/group-list-members?view=graph-rest-1.0&tabs=http).
 
 ## SYNTAX