On the Bootstrap website, they give a recommended HTML structure. We'll be interpolating from their recommendation to use Bootstrap code provided through the CDN to instead use the local copies of Bootstrap, jQuery, and Popper that we just installed. Refer to the Getting started page at http://getbootstrap.com/docs/4.0/getting-started/introduction/.
What we'll do is modify views/layout.hbs to match their recommended template:
<!doctype html><html lang="en"> <head> <title>{{title}}</title> <meta charset="utf-8"> <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to- fit=no"> <link rel="stylesheet" href="/assets/vendor/bootstrap/css/bootstrap.min.css"> <link rel='stylesheet' ...