MINOR: Update introduction.html
<p>To understand how Kafka does these things, let's dive in and explore Kafka's capabilities from the bottom up.</p>
<p>First a few concepts:</p>
<ul>
- <li>Kafka is run as a cluster on one or more servers that can span multiple datacenters.
+ <li>Kafka runs as a cluster on one or more servers that can span multiple datacenters.
<li>The Kafka cluster stores streams of <i>records</i> in categories called <i>topics</i>.
<li>Each record consists of a key, a value, and a timestamp.
</ul>
