Available in Chrome 42+ (for Android)
The web app install banner will prompt the user to add your web app to the users home screen. It will only prompt when a number of criteria have been met:
short_name, 144 pixel icon and a type of 'image/png'
To see if this example works, come back in another day and you will see the banner.
For testing we encourage you to force the banner to appear by setting the chrome://flags/#bypass-app-banner-engagement-checks flag.