how to add badge number that increases every time item is added in cart bootstrap 4 code example

Example 1: bootstrap Pill badges

Use the .badge-pill modifier class to make badges more rounded 
(with a larger border-radius and additional horizontal padding). 
Useful if you miss the badges from v3.

<span class="badge badge-pill badge-primary">Primary</span>
<span class="badge badge-pill badge-secondary">Secondary</span>
<span class="badge badge-pill badge-success">Success</span>
<span class="badge badge-pill badge-danger">Danger</span>
<span class="badge badge-pill badge-warning">Warning</span>
<span class="badge badge-pill badge-info">Info</span>
<span class="badge badge-pill badge-light">Light</span>
<span class="badge badge-pill badge-dark">Dark</span>

Example 2: bootstrap Badges

Badges scale to match the size of the immediate parent element by 
using relative font sizing and em units.
<h1>Example heading <span class="badge badge-secondary">New</span></h1>
<h2>Example heading <span class="badge badge-secondary">New</span></h2>
<h3>Example heading <span class="badge badge-secondary">New</span></h3>
<h4>Example heading <span class="badge badge-secondary">New</span></h4>
<h5>Example heading <span class="badge badge-secondary">New</span></h5>
<h6>Example heading <span class="badge badge-secondary">New</span></h6>
<button type="button" class="btn btn-primary">
  Profile <span class="badge badge-light">9</span>
  <span class="sr-only">unread messages</span>
</button>