ref-manual: Added utils class.

(From yocto-docs rev: ba1c91587a272bc285867b0d7d8c1fe8d73b809e)

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

@@ -2718,6 +2718,23 @@
     </para>
 </section>
 
+<section id='ref-classes-utils'>
+    <title><filename>utils.bbclass</filename></title>
+
+    <para>
+        The <filename>utils</filename> class provides some useful Python
+        functions that are typically used in inline Python expressions
+        (e.g. <filename>${@...}</filename>).
+        One example use is for <filename>base_contains()</filename>.
+    </para>
+
+    <para>
+        This class is enabled by default because it is inherited by the
+        <link linkend='ref-classes-base'><filename>base</filename></link>
+        class.
+    </para>
+</section>
+
 <section id='ref-classes-externalsrc'>
     <title><filename>externalsrc.bbclass</filename></title>