[Vuejs]-What is the best way to integrate bootstrap theme on VueJS

Adding the Bootstrap CSS file like any other CSS file in the head of index.html should work (cf Bootstrap docs):

<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css" integrity="sha384-WskhaSGFgHYWDcbwN70/dfYBj47jz9qbsMId/iRN3ewGhXQFZCSftd1LZCfmhktB" crossorigin="anonymous">

No need to include the fonts, the CSS will get them.