Clarify h2 HTML heading descriptions

seed/challenges/01-front-end-development-certification/html5-and-css.json

@@ -86,8 +86,7 @@
         "Over the next few challenges, we'll build an HTML5 app that will look something like this:",
         "<a href=\"//i.imgur.com/jOc1JF1.png\" data-lightbox=\"img-enlarge\"><img class=\"img-responsive\" src=\"//i.imgur.com/jOc1JF1.png\" title=\"Click to enlarge\" alt=\"A screen shot of our finished Cat Photo App\"></a>",
         "The <code>h2</code> element you enter will create an <code>h2</code> element on the website.",
-        "This element tells the browser how to render the text that it contains.",
-        "<code>h2</code> elements are slightly smaller than <code>h1</code> elements. There are also <code>h3</code>, <code>h4</code>, <code>h5</code> and <code>h6</code> elements.",
+        "This element tells the browser about the structure of your website. <code>h1</code> elements are often used for main headings, while <code>h2</code> elements are generally used for subheadings. There are also <code>h3</code>, <code>h4</code>, <code>h5</code> and <code>h6</code> elements to indicate different and new sections.",
         "Add an <code>h2</code> tag that says \"CatPhotoApp\" to create a second HTML <code>element</code> below your \"Hello World\" <code>h1</code> element."
       ],
       "challengeSeed": [