Update the prototype footer a little bit.

Prototype/email.html

@@ -117,6 +117,10 @@ <h6>Comments</h6>
             <p>Adds a new task to the list.</p>
             <p>For example, to add a task "Buy eggs at Wallmart", reply with</p>
             <p><code>Add: Buy eggs at Wallmart</code></p>
+            <p>You can use <a href="http://daringfireball.net/projects/markdown/syntax">Markdown</a> formatting for the task.</p>
+            <p><code>Add: **Buy eggs** at [Wallmart](http://...)</code></p>
+            <p>You can add a due date or assign the task to a person, using one of the following syntaxes:</p>
+            <p><code>Add: Buy eggs [due: tomorrow][assigned to: Jim]</code></p>
           </dd>
 
           <dt class="footer__instructions__list__instruction-command">Delete [number of the task]</dt>