Add a note about the need of CSS to the examples in README

[saikyun]

trafficstars

Is your feature request related to a problem? Please describe.

It took me a while to realize that the slider didn't show up because of missing CSS, rather than some other error. :)

Describe the solution you'd like

Put a note in the readme (e.g. right below the examples) that you need additional CSS to see the slider.

[CarlosAmaral]

https://github.com/tomkp/react-split-pane#example-styling

[jmtimko5]

Strongly agree, most libraries ship with default styling. I think making people uptake the example styling or provide their own is fine, just explain that in the README.

[raptoria]

I had this same problem

[mawisome]

Wow. I had to find this issue to understand, that the separate css is needed. Now, after I know that it is needed, I like this feature that you can style the splitters yourself.