trying out d3

Something that's maybe a little confusing at first about d3 is that `.enter().append()` and `selection.append()` mean slightly different things. `.enter().append()` will append a new DOM element to `selection` for each new data element. `selection.append()` will append a new *child* DOM element to each element in `selection`. I think you wanted to latter here.

Problem is, if we did just a `selection.append('text')` here, another child `<text>` element would appear whenever we call the circle function (so we would end up with more than one). To solve this, we would append the text element only to the circle elements newly created from `.enter().append('circle')` above.