title: Using consecutive D3.html() methods to concatenate html; rather than replace
body: <p>I want to use d3.html() to add html to a div selector. And then I'd like to use it a second time, to append more html.</p>
  
  <p>The problem is, when you use d3.html() on a selection, you completely replace the html attached to the object selector. </p>
  
  <p>Is there a way to use html to append more html, rather than entirely replace the prior html?</p>