docs: add a sentence to quasi-delete docs

diff --git a/doc/manual.xml.head b/doc/manual.xml.head
index d65fe8fffbb33761e88bd63d584fdbdbfba26a3c..07ab5db694fb3a202c9d9454a6903317afd94d8b 100644 (file)
--- a/doc/manual.xml.head
+++ b/doc/manual.xml.head
@@ -13391,7 +13391,9 @@ color progress white red
         <title>Introduction</title>
         <para>The
         <quote>quasi-delete</quote> function marks an email that should be
-        hidden from the index, but NOT deleted.</para>
+        hidden from the index, but NOT deleted.  The email will disappear from
+        the index when <link linkend="index-map">&lt;sync-mailbox&gt;</link> is
+        called.</para>
         <para>On its own, this feature isn't very useful. It forms a useful
         part of the notmuch plugin.</para>
       </sect2>