link to attestation tutorial page

static/usage.html

@@ -35,6 +35,8 @@
         <div id="content">
             <h1>Usage</h1>
             <p><strong>This page is currently a placeholder and will be filled with lots of content over time.</strong></p>
+            <h2>Auditor</h2>
+            <p>See the <a href="https://attestation.app/tutorial">tutorial page on the site for the attestation sub-project</a>.</p>
         </div>
         <footer>
             <a href="/"><img src="https://grapheneos.org/logo.png" width="512" height="512" alt=""/>GrapheneOS</a>