Style Guide: list e.g., and i.e., in the grammar section

Author: domfarolino

whatwg.org/style-guide

@@ -66,6 +66,7 @@
  <li>Use the <a href="https://en.wikipedia.org/wiki/Serial_comma">Oxford Comma</a>.</li>
  <li>Avoid "one of" unless it's followed by a bulleted list. You can normally leave it out and just use "or". If you cannot leave it out, that might be a good indication you want to use a bulleted list for clarity.</li>
  <li>"A hierarchy" (not "an").</li>
+ <li>Use e.g., and i.e., instead of their non-comma-ending variants.</li>
 </ul>
 
 <h2 id="casing">Casing<a class="self-link" href="#casing"></a></h2>