Update New-AzSynapseRoleAssignment.md (Azure#20905)

Author: meenalsri

src/Synapse/Synapse/help/New-AzSynapseRoleAssignment.md

@@ -9,6 +9,7 @@ schema: 2.0.0
 
 ## SYNOPSIS
 Creates a Synapse Analytics role assignment.
+ 
 
 ## SYNTAX
 
@@ -76,6 +77,9 @@ The cmdlet may call below Microsoft Graph API according to input parameters:
 * GET /users/{id}
 * GET /servicePrincipals/{id}
 
+>[!Note]
+> To create a role assignment for a service principal, pass the object ID of the principal in the ObjectId parameter.
+
 ## EXAMPLES
 
 ### Example 1