chore(readme): added bs4 cdn instructions (#1784)
chore(readme): added bs4 cdn instructions (#1784)

* Include CDN instructions for Bootstrap 4

* chore(readme): added bs4 cdn instructions

valor-software/ng2-bootstrap,erodriguezh/ngx-bootstrap,Le0Michine/ng2-bootstrap,valor-software/ngx-bootstrap,valor-software/ngx-bootstrap,valor-software/ngx-bootstrap,IlyaSurmay/ngx-bootstrap-versioning,IlyaSurmay/ngx-bootstrap-versioning,Le0Michine/ng2-bootstrap,valor-software/ngx-bootstrap,valor-software/ng2-bootstrap