run on terminal
yarn add @fortawesome/fontawesome-free
import on application.scss
$fa-font-path: '@fortawesome/fontawesome-free/webfonts';
@import '@fortawesome/fontawesome-free/scss/fontawesome';
@import '@fortawesome/fontawesome-free/scss/solid';
@import '@fortawesome/fontawesome-free/scss/regular';
@import '@fortawesome/fontawesome-free/scss/brands';
@import '@fortawesome/fontawesome-free/scss/v4-shims';
[optional] import on aaplication.js
import "@fortawesome/fontawesome-free/js/all";