Are you still having trouble getting the jar to show? Getting the file structure right definitely seems frustrating :|
This seems to be the sort of applet wrapping and whatnot that itch does on their end. Meaning the entry point they need is the class that either 1) runs the main class that you first call in your application, or 2) is defined in your (Web Start?) settings as the launch applet.
Basically, whatever class starts your game is what they need. (If they want the package as well, it'd be something like myPackageName.myFirstClassName instead, or possibly myPackageName.myFirstClassName.class since they don't seem to add the .class on their end.) I'm not sure if they actually need that "io.itch." before everything or if it was just an example.
You'll have to play around with it and see what works :o
\ \ Just as an aside, since it looks like you were using them in "Fly Squirrel Fly": I also read that jFrames do not run on their own in browsers; they need to be replaced with jApplets (which are the web equivalent & function similarly) for web use. That may be the issue if you have the class right but it's not running.
(Again, I haven't done applets before, so double-check my facts here lol.)