Add extended headers in the prose example

docs/_includes/markdown-prose.md

@@ -191,6 +191,11 @@ Another thing I’ve done in the past is put a `code` tag inside of a link, like
 
 Phew, with any luck we have styled the headings above this text and they look pretty good.
 
+##### We should also make sure we're styling `h5` elements as well.
+
 Let’s add a closing paragraph here so things end with a decently sized block of text. I can’t explain why I want things to end that way but I have to assume it’s because I think things will look weird or unbalanced if there is a heading too close to the end of the document.
 
+###### And, finally, an `h6`.
+Ultimately, though, we also want to support the `h6` headers.
+
 What I’ve written here is probably long enough, but adding this final sentence can’t hurt.