UI: Add a note mentioning the read-only situation

templates/default-layout.hamlet

@@ -77,6 +77,10 @@ $# <http://creativecommons.org/publicdomain/zero/1.0/>.
             <code>
               #{h}
 
+  <div>
+    NOTE: Due to big changes happening in the app, this instance is currently
+    read-only, federation is disabled, and some UIs have been removed.
+
   <.instance>
     Vervis @ #{renderAuthority instanceHost}