ref-manual: Added spdx class.

(From yocto-docs rev: 1b7f65f6b48050190cc04bba07f3501ad119adbb)

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

@@ -1934,6 +1934,20 @@
     </para>
 </section>
 
+<section id='ref-classes-spdx'>
+    <title><filename>spdx.bbclass</filename></title>
+
+    <para>
+        The <filename>spdx</filename> class integrates real-time license
+        scanning, generation of SPDX standard output, and verification
+        of license information during the build.
+        <note>
+            This class is currently at the prototype stage in the 1.5
+            release.
+        </note>
+    </para>
+</section>
+
 <section id='ref-classes-package_tar'>
     <title><filename>package_tar.bbclass</filename></title>