After exporting with Output set to Multi-device Web App (iPad, iPhone, Android), look in html5_output\assets\images. You'll find the images that are used for the web installation for each of those devices. If you export with the output set to just one of those devices, then only the image for that particular device will be there.
You can replace those images with your own--just make sure they're the same name and in the same location. Your images could then include the instructions for each browser for those devices.
Yes, I was hoping there might be an option within in5, or a snippet of code already written within the help pages, but I can't find anything.
I'll try and find somebody with that knowledge Thank you