ref-manual: Added reference for npm.bbclass.

(From yocto-docs rev: 7bf6401ad16ad83743d82a3b7592f77237c453f8)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/ref-classes.xml

@@ -2251,6 +2251,20 @@
     </para>
 </section>
 
+<section id='ref-classes-npm'>
+    <title><filename>npm.bbclass</filename></title>
+
+    <para>
+        Provides support for building Node.js software fetched using the npm
+        package manager.
+        <note>
+            Currently, recipes inheriting this class must use the
+            <filename>npm://</filename> fetcher to have dependencies fetched
+            and packaged automatically.
+        </note>
+    </para>
+</section>
+
 <section id='ref-classes-oelint'>
     <title><filename>oelint.bbclass</filename></title>