add font awesome link in css code example

Example 1: link font awesome html

<link
      rel="stylesheet"
      href="https://use.fontawesome.com/releases/v5.13.0/css/all.css"
      integrity="sha384-Bfad6CLCknfcloXFOyFnlgtENryhrpZCe29RTifKEixXQZ38WheV+i/6YWSzkz3V"
      crossorigin="anonymous"
    />

Example 2: font awesome cdn

<link rel="stylesheet" type="text/css" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.4.0/css/font-awesome.min.css">