Update README.md

A more interesting example where the state is being updated every second.

While trying to use the package, I initially tried doing the re-rendering with `root.update(render(), const v.Context(true))`. But that didn't actually work... it simply started adding the new divs at the end. Initially I figured that I had a bug in some of my rendering ... etc. Basically, to avoid misunderstanding how to use this library in a more complicated scenario, I made this example.

Although, `root.update(render(), const v.Context(true))` would be easier to use.

Also, I would have liked to create an example where you also have event handlers, but I couldn't figure out how to do it, or whether it's possible to do it at all. I.e. create a virtual button with onClick that increments the count.