Improving the readme example

[dbramwell]

Hi,

Thanks for this, I started using flutter today after not getting the performance I needed out of react-native. I was super pleased to see that there was a dart port of roughjs!

When I was trying to follow the examples I was just using:

Paint paint = Paint();
paint.color = Color(0xff6ab04c);

I wasn't getting the look that I'd hoped for, it looked a lot different than the roughjs equivalent. Eventually I found in your example project you specify style = PaintingStyle.stroke. I wondered if it'd be worth adding that to the readme?

I'm sure if I wasn't a complete flutter noob I would have know about this Paint param, but might be nice having a fully working example in the readme anyway?