Simply publish an index.html file as a public asset and you will then have a public-facing website for your Domo app. Creating public assets is as simple as adding a new folder to your custom Domo app project called "public-assets". Any file that exists within the "public-assets" folder, when published up to your Domo instance and instantiated as a card, will now be available to the public. The URL for your public asset will be the same URL that you find as the `src` for the iframe that hosts your Domo app as a card in your instance.
For more information on the Public Domo App Assets, see https://www.developer.domo.com.