import css file in the example of usage

[wujr5]

A css file is included when importing the package. You may have to setup your bundler to embed the css in your page.

Warning is not enough, the statement of importing css file should clearly show in the example of usage.

At the same time, tippy.js is include by your source code, so it is not necessary included in the installation guide.

[Denia-park]

thank you bro.

Thanks to your PR, I was able to find the css file

[Joaos98]

+1, also had trouble importing the css file until i saw this PR, thank you so much!