Backend class alias on user:sync #853

WHAT Needs to be Documented?

occ user:sync command has now aliases for backend classes
owncloud/core#40640

WHERE Does This Need To Be Documented (Link)?

WHY Should This Change Be Made?

(Optional) What Type Of Content Change Is This?

• New Content Addition
• Old Content Deprecation
• Existing Content Simplification
• Bug Fix to Existing Content

(Optional) Which Manual Does This Relate To?

• Admin Manual
• Developer Manual
• User Manual
• Android
• iOS
• Branded Clients
• Desktop Client
• Other