Add a new section about version bumps necessary when new major release

branches (RELENG_X) are created.  Add stable-supfile as first entry.

Suggest by:	dougb

en_US.ISO8859-1/articles/releng/article.sgml

@@ -443,6 +443,25 @@
 
     </sect3>
 
+    <sect3 id="versionbump-major">
+      <title>Preparing a new major release branch
+        (RELENG_<replaceable>X</replaceable>)</title>
+
+      <para>When a new major release branch, such as
+        <literal>RELENG_6</literal> is branched from HEAD, some
+	additional files must be updated before releases can be made
+	from this new branch.</para>
+
+      <itemizedlist>
+	<listitem>
+          <para><filename>src/share/examples/cvsup/stable-supfile</filename>
+- must be updated to point to the new -STABLE branch, when
+applicable.</para>
+        </listitem>
+      </itemizedlist>
+
+    </sect3>
+
     <sect3>
       <title>Creating Release Tags</title>