Add more details on README regarding usage

[Jefferson227]

Hi, I'm pretty new to React and started to use this library in a personal project. When I installed the Bloomer along with Bulma, I created a component that was being rendered but the Bulma's CSS wasn't loaded.

Then, I just imported Bulma into the index.js and it rendered perfectly.

I don't know if all the React developers knows that, but for me, as a begginer, I had this difficult. So this instruction might be useful for other begginers too.

If you will accept my contribution, please consider do the same change on the website: https://bloomer.js.org/#/documentation/overview/start

Thanks :)

[coveralls]

Coverage remained the same at 100.0% when pulling a83a4cf65518bdbb3c738e0fd432a3bd6bba5806 on Jefferson227:master into b9af8271840c9a52ecf493f3b1f919d8cd3e5fc1 on AlgusDark:master.

[sidney-pham]

Might need to be import 'bulma/css/bulma.css'; for certain setups.