Add a note about which options default to on.

Submitted by:	bapt (original version)
Reviewed by:	bapt
Approved by:	joel (mentor)

en_US.ISO8859-1/books/porters-handbook/book.xml

@@ -4546,6 +4546,34 @@ CONFIGURE_ARGS+=	--with-foo
 	      Do not use this method for new ports.</para>
 	  </important>
 	</sect3>
+
+	<sect3>
+	  <title>Default Options</title>
+  	  <para>The following options are always on by default.</para>
+          <itemizedlist>
+	    <listitem>
+	      <para><literal>DOCS</literal> &mdash; build and install
+		documentation.</para>
+	    </listitem>
+	    <listitem>
+	      <para><literal>NLS</literal> &mdash; Native Language
+		Support.</para>
+            </listitem>
+	    <listitem>
+	      <para><literal>EXAMPLES</literal> &mdash; build and install
+		examples.</para>
+	    </listitem>
+	    <listitem>
+	      <para><literal>IPV6</literal> &mdash; IPv6 protocol support.</para>
+	    </listitem>
+	  </itemizedlist>
+	  <note>
+	    <para>There is no need to add these to
+	      <makevar>OPTIONS_DEFAULT</makevar>.  To have them show up
+	      in the options selection dialog, however, they must be added
+	      to <makevar>OPTIONS_DEFINE</makevar>.</para>
+          </note>
+	</sect3>
       </sect2>
 
       <sect2>