I've created a custom module that creates a jumbotron custom block type. The module has an empty .module file and a dir config/install with many .yml files. This works great when I install and create blocks. I can even place my block--bundle--jumbotron.html.twig in the templates folder of the theme and styling works great! I would like this twig file included in the module and many tutorials explain how to do this if you have a build function in your module, I do not. The module is just creating a block type for me.