I installed vue using vue-cli, with

   vue init webpack testproject   
   cd testproject   
   npm update

Then I added the vue2-bootstrap4 npm package as documented on https://www.npmjs.com/package/vue2-bootstrap4 ) .

   npm install --save-dev vue2-bootstrap4

I tried the button-group example. First it didn't work at all, I had to add bootstrap itself by doing

   npm install --save-dev bootstrap@4.0.0-alpha.5

.. and adding this to my .vue file:

   import 'bootstrap/dist/css/bootstrap.min.css'

The button-group example works. But the navbar example doesn't, the javascript console shows:

Vue warn: Failed to mount component: template or render function not defined. (found in component <bNav>)

Mike.