Fix broken domkit documentation

[tobil4sk]

Closes #84.

The css sample needs to have an actual component to avoid the "Unknown property padding" error.

It would be nice if the css sample could be:

sample-view.box {
    padding : 20;
    background : #400;
}

But since the sample-view component is not in a registered path, there will be an error during the compile time css check. So it's simpler to just use flow so that the documentation doesn't become too complex:

flow.box {
    padding : 20;
    background : #400;
}