...to the Extending Qt Creator Manual

Change-Id: I85dea1d815037af8334aed09c7b4ad8611d4170c
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Tarja Sundqvist <tarja.sundqvist@qt.io>
Reviewed-by: Topi Reiniö <topi.reinio@qt.io>