Update concept-authentication-methods-manage.md

Add preview tag to migration control

Author: jpettere

articles/active-directory/authentication/concept-authentication-methods-manage.md

@@ -75,7 +75,7 @@ For users who are enabled for **Mobile phone** for SSPR, the independent control
 
 Similarly, let's suppose you enable **Phone call** for a group. After you enable it, you find that even users who aren't group members can sign-in with a voice call. In this case, it's likely those users are enabled for **Mobile phone** in the legacy SSPR policy or **Call to phone** in the legacy MFA policy.  
 
-## Migration between policies
+## Migration between policies (preview)
 
 The Authentication methods policy provides a migration path toward unified administration of all authentication methods. All desired methods can be enabled in the Authentication methods policy. Methods in the legacy MFA and SSPR policies can be disabled. Migration has three settings to let you move at your own pace, and avoid problems with sign-in or SSPR during the transition. After migration is complete, you'll centralize control over authentication methods for both sign-in and SSPR in a single place, and the legacy MFA and SSPR policies will be disabled.