Hello D.,
Awaitting the feature (for space management between title and diagram);
A funny workaround is to add a first step, with hidden link with the rest of the diagram, as:
#MintCream:<b><size:15>Activity Diagram for User Management;
-[hidden]-> \t ;
[Click to see full code on PlantUML server]
If that can help,
Regards,
Th.