clarification about local builds and signing

static/articles/grapheneos-servers.html

@@ -37,6 +37,10 @@
 
             <p>This is a detailed list of the public GrapheneOS servers.</p>
 
+            <p>We use hardened local machines for building and signing rather than servers outside
+            our physical control, so information on that infrastructure is outside the scope of this
+            page but may be provided in the future elsewhere.</p>
+
             <nav id="table-of-contents">
                 <h2><a href="#table-of-contents">Table of contents</a></h2>