There are at least two methods to get this done. Here's the method I used and below is the outline of a method I found in the book Mastering Drupal 8.
This is a simple overriding process. Get a copy of the page.html.twig from the Bootstrap parent theme folder and copy it into our subtheme/templates directory.
First, we need to create a jumbotron region. This can be accomplished by modifying the page.html.twig file with the following snippet.
Above the #Main section, we'll paste this block. Use your own image
{# Jumbotron #}
