I apologize but the quoted comment is unfortunatelly misleading, and I will update it.
At this moment we do not plan to add it, because it is already handled by the Doctrine internal functions and we want to avoid duplicating the already available functionality. You can however use Skippers external tools to generate getters and setters, see the tutorial how to set up External tools.
DoctrineExtensions are not fully supported at this moment. We are already cooperating with the author to achieve full support, but we will need to rework big part of the DoctrineExtensions logic and this will take some time. At the moment you can combine Skipper and DoctrineExtensions when you use the annotations format - behaviors will have to be written by hand, but they will not be lost or damaged when you import/export the definitions from Skipper.