Extract the file and look at the file structure. It will consist of some examples.
A Web App can consist of:
HTML files
Images
Javascript (include the ls-links.js file)
CSS
Font Files
Anything that you usually use to make a website!
Instead of naming the HTML file index.html name the HTML to entrypoint_default.html. This will allow Ubiquity to detect that you're using an Integrated Web App inside your app.
Zip the folder and contents. A folder might look something like this: