Slightly improved Readme examples

[rrmn]

• added {closest_state} to title of example 1 -> makes the graphic understandable at first glance and shows this crucial variable in the code
• added names to code chunks -> graphics don't get saved under unnamed-chunk.gif

[thomasp85]

My reason for not adding labels to the first example was to keep it absolutely minimal... labelling is introduced in the next example, so I think that's ok..?

[rrmn]

Totally agree with the minimal approach. The issue: the example is not intuitively comprehensible as it stands. Right now it is really, really hard to understand what is going on in the gif. Can you think of an alternative way to clarify it more?

The PR is based on my own learning curve and questions that have popped up from colleagues and on SO. Using labelling was an attempt to kill two birds with one stone (easier comprehension + closest state).

[thomasp85]

That makes sense... I'll try to think of a better minimal example...