- Add a brief note on the "developer mode" for porting

Requested by:	bapt

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

@@ -125,6 +125,18 @@
 	too.</para>
     </note>
 
+    <note>
+      <para>It is recommended to set the <makevar>DEVELOPER</makevar>
+	&man.make.1; variable in <filename>/etc/make.conf</filename>
+	before getting into porting.</para>
+
+      <screen>&prompt.root; <userinput>echo DEVELOPER=yes >> /etc/make.conf</userinput></screen>
+
+      <para>This setting enables the <quote>developer mode</quote> that
+	displays deprecation warnings and activates some further quality
+	checks on calling the <command>make</command> command.</para>
+    </note>
+
     <sect1 id="porting-makefile">
       <title>Writing the <filename>Makefile</filename></title>