documentation/poky-ref-manual/ref-classes.xml: documented useradd.bbclass

New section per Paul Eggleton's request.

(From yocto-docs rev: ffedb53e5c706cffb83978f1704a606d29233e36)

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

documentation/poky-ref-manual/ref-classes.xml

@@ -422,6 +422,21 @@
     </para>
 </section>
 
+<section id='ref-classes-useradd'>
+    <title>Adding Users - <filename>useradd.bbclass</filename></title>
+
+    <para>
+        If you have packages that install files that are owned by custom users or groups, 
+        you can use this class to specify those packages and associate the users and groups
+        with those packages.
+        The <filename>meta-skeleton/recipes-skeleton/useradd/useradd-example.bb</filename> 
+        recipe in the Yocto Project Files provides a simple exmample that shows how to add three 
+        users and groups to two packages.
+        See the <filename>useradd-example.bb</filename> for more information on how to 
+        use this class.
+    </para>
+</section>
+
 <section id='ref-classes-others'>
     <title>Other Classes</title>
 
@@ -499,7 +514,6 @@
         tinderclient.bbclass
         toolchain-scripts.bbclass
         typecheck.bbclass
-        useradd.bbclass
         utility-tasks.bbclass
         utils.bbclass
 -->