There are two options. Either have the actual widget yaml in code fences under the resource heading or have a link directly to the yaml file (e.g., github raw view link). The MainUI marketplace code can then extract the yaml code for direct installation. As of right now, there are no other mechanisms that work.
These will still have to be manually downloaded and installed by the user. Complex widgets like this are just always going to have slightly more complex installations.
You’ve got all the images as pngs, if you created those pngs from svg or recreated the images as svgs, then you could use something like this system to directly incorporate the images into the widget. That is a lot more work, however.