Escape angle brackets to fix missing placeholder

Without backslashes in front of the angle brackets, <UserIdentity> was interpreted as a (disallowed) HTML tag, and the placeholder did not appear in the published page.

Author: garycentric

exchange/exchange-ps/exchange/Start-ManagedFolderAssistant.md

@@ -130,7 +130,7 @@ The Identity parameter specifies the mailbox to be processed. In cross-premises
 - SamAccountName
 - User ID or user principal name (UPN)
 
-**Note**: In the cloud-based service, if you receive an error, try using the mailbox GUID for the value of this parameter. You can get the mailbox GUID value by replacing <UserIdentity> with the email address of the user and running the following command: `Get-Mailbox -User <UserIdentity> | Format-List *GUID,MailboxLocations`.
+**Note**: In the cloud-based service, if you receive an error, try using the mailbox GUID for the value of this parameter. You can get the mailbox GUID value by replacing \<UserIdentity\> with the email address of the user and running the following command: `Get-Mailbox -User <UserIdentity> | Format-List *GUID,MailboxLocations`.
 
 ```yaml
 Type: MailboxOrMailUserIdParameter