Adding Announcement

The following html can be used to add an announcement to the front page of the site

<div style="padding: 1rem 2rem;font-size: 0.9rem;background: #e1eade;border-bottom: 1px solid #ddd;">
<strong style="color: #46ab26;border-bottom: 1px solid;margin: 0 0 0.5rem 0;display: inline-block;
">Update: New build system</strong><br>
QuantEcon is currently building a new way of constructing the website. This is the first release under this new build
pathway so if you spot any errors please leave comments at <a href="mailto:contact@quantecon.org">contact@quantecon.org</a><br>
</div>