Updated documentation

I took the liberty to update the `README` a bit, to make starting using TiCalabash easier. (hopefully).

I added references to the Calabash documentation and took parts out of the Slideshare presentation. I also ran the examples and added some clarification on points where I got stuck. I added the part about `sudo`, because @ronaldtreur had the same issue and posted another workaround during his presentation at the Amsterdam Titanium Meetup. I liked your better :)