add introduction to donate page

static/donate.html

@@ -46,6 +46,14 @@
         <main id="donate">
             <h1><a href="#donate">Donate</a></h1>
 
+            <p>GrapheneOS is an open source project supported via donations from individuals,
+            companies and other organizations. Donations are used for paying developers,
+            purchasing hardware (workstations, test devices, debugging cables/boards, etc.),
+            paying for infrastructure (domains, virtual/dedicated servers) and paying legal
+            fees.</p>
+
+            <p>The multiple ways to donate are listed in the sections on this page.</p>
+
             <nav id="table-of-contents">
                 <h2><a href="#table-of-contents">Table of contents</a></h2>