updated DC requirements for Cloud Kerberos Trust

requirements updated to more explicitly call out minimum Windows Server version to match /windows/security/identity-protection/hello-for-business/hello-hybrid-cloud-kerberos-trust

Author: PhillyUrbs

articles/active-directory/authentication/howto-authentication-passwordless-security-key-on-premises.md

@@ -44,7 +44,7 @@ You must also meet the following system requirements:
 
 - Devices must be running Windows 10 version 2004 or later.
 
-- Your Windows Server domain controllers must have patches installed for the following servers:
+- Your Windows Server domain controllers must run Windows Server 2016 or later and have patches installed for the following servers:
     - [Windows Server 2016](https://support.microsoft.com/help/4534307/windows-10-update-kb4534307)
     - [Windows Server 2019](https://support.microsoft.com/help/4534321/windows-10-update-kb4534321)