explain the usage guide

static/usage.html

@@ -42,8 +42,10 @@
             <h1 id="usage">
                 <a href="#usage">Usage</a>
             </h1>
-            <p><strong>This guide is still very new and will be filled with lots of additional
-            content over time.</strong></p>
+            <p>This is a guide covering some aspects of using GrapheneOS. It's not intended to be
+            an overview of the privacy and security features implemented by GrapheneOS. It will
+            only cover the user-facing impact of features, and most of the privacy and security
+            work is done under the hood.</p>
 
             <h2 id="table-of-contents">
                 <a href="#table-of-contents">Table of contents</a>