ref-manual: Added the linux-kernel-base class.

(From yocto-docs rev: 32355612d393696b48634bb67569b890c1315593)

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

@@ -1030,6 +1030,18 @@
     </para>
 </section>
 
+<section id='ref-classes-linux-kernel-base'>
+    <title><filename>linux-kernel-base.bbclass</filename></title>
+
+    <para>
+        The Linux kernel base (<filename>linux-kernel-base</filename>) class
+        provides common functionality for recipes that build out of the Linux
+        kernel source tree.
+        These builds goes beyond the kernel itself.
+        For example, the Perf recipe also inherits this class.
+    </para>
+</section>
+
 <section id='ref-classes-mime'>
     <title><filename>mime.bbclass</filename></title>