ref-manual: Added gtk-doc class.

(From yocto-docs rev: debb03e8934b8a8b0f07e7c583aa712bacacfe74)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/ref-classes.xml

@@ -719,6 +719,17 @@
     </para>
 </section>
 
+<section id='ref-classes-gtk-doc'>
+    <title><filename>gtk-doc.bbclass</filename></title>
+
+    <para>
+        The GIMP Toolkit Documentation (<filename>gtk-doc</filename>) class
+        is a helper class to pull in the appropriate
+        <filename>gtk-doc</filename> dependencies and disable
+        <filename>gtk-doc</filename>.
+    </para>
+</section>
+
 <section id='ref-classes-gtk-icon-cache'>
     <title><filename>gtk-icon-cache.bbclass</filename></title>