adding bootstrap 4 to symfony code example

Example: bootstrap in symfony using sass

Importing Bootstrap Styles using sass.

yarn add bootstrap

Now that bootstrap lives in your node_modules/ directory, you can import it from any Sass or JavaScript file. For example, if you already have a global.scss file, import it from there:
the ~ allows you to reference things in node_modules
@import "~bootstrap/scss/bootstrap";

That's it! This imports the node_modules/bootstrap/scss/bootstrap.scss file into global.scss.
You can even customize the Bootstrap variables first!