Mention styles in README.md

[kumavis]

The styles need to be manually included (correct?)
This is not mentioned in the doc

[kumavis]

consider adding them when injecting the code mirror

var fileref=document.createElement("link")
fileref.setAttribute("rel", "stylesheet")
fileref.setAttribute("type", "text/css")
fileref.setAttribute("href", filename)
document.getElementsByTagName("head")[0].appendChild(fileref)