The support added was the Croogo/Core theme for baking plugins. It creates a workable Croogo plugin skeleton including a sample Dashboard widget. There were a few PR's starting around
#963 where this code was updated / added.
./bin/cake bake plugin -t Croogo/Core <PluginName>
I don't recall if the automatic re-build of the autoloader is in place in version 4, so you might have to follow this up by building it manually (this will have effect only if you allowed bake to modify your composer.json file to require the new plugin).
composer dump-autoload -o
After that, you will need to enable the plugin in the Extensions > Plugins admin page.