Clarify behavior of HTML toggle bar. See Carl Schwan's commit 6c10959b in PIM messagelib.

doc/kmail2/configure.docbook

@@ -2076,8 +2076,7 @@ dialog. You may choose any or all of six options.</para>
             <para>
               You can still easily view messages in &HTML; format by
               clicking the plain message/HTML message toggle bar on the left hand side of the preview pane.
-              Please see <link linkend="configure-appearance-general">the General tab</link>
-              on the <guilabel>Appearance</guilabel> page to enable this feature.
+              This bar will not be visible unless the message you are viewing contains &HTML; content.
             </para>
 	  </listitem>
 	</varlistentry>