document another way to add dashboard action
document another way to add dashboard action

ARTACK/SonataAdminBundle,greg0ire/SonataAdminBundle,ARTACK/SonataAdminBundle,peter-gribanov/SonataAdminBundle,peter-gribanov/SonataAdminBundle,Armstrong1992/SonataAdminBundle,Armstrong1992/SonataAdminBundle,OskarStark/SonataAdminBundle,mweimerskirch/SonataAdminBundle,jordisala1991/SonataAdminBundle,ossinkine/SonataAdminBundle,osavchenko/SonataAdminBundle,ARTACK/SonataAdminBundle,mweimerskirch/SonataAdminBundle,sonata-project/SonataAdminBundle,ossinkine/SonataAdminBundle,sonata-project/SonataAdminBundle,OskarStark/SonataAdminBundle,greg0ire/SonataAdminBundle,osavchenko/SonataAdminBundle,ARTACK/SonataAdminBundle,osavchenko/SonataAdminBundle,peter-gribanov/SonataAdminBundle,ossinkine/SonataAdminBundle,peter-gribanov/SonataAdminBundle,jordisala1991/SonataAdminBundle,OskarStark/SonataAdminBundle,ossinkine/SonataAdminBundle,osavchenko/SonataAdminBundle,osavchenko/SonataAdminBundle,greg0ire/SonataAdminBundle,jordisala1991/SonataAdminBundle,greg0ire/SonataAdminBundle,mweimerskirch/SonataAdminBundle,OskarStark/SonataAdminBundle,mweimerskirch/SonataAdminBundle,jordisala1991/SonataAdminBundle