doc-guide: kernel-doc: add examples about nested union/structs

It helps to give some examples about how to use in-line
comments also when nested union/structs are present. So add it.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/doc-guide/kernel-doc.rst

@@ -286,9 +286,18 @@ on a line of their own, like all other kernel-doc comments::
          * Here, the member description may contain several paragraphs.
          */
         int baz;
+        union {
                 /** @foobar: Single line description. */
                 int foobar;
         };
+        /** @bar2: Description for struct @bar2 inside @foo */
+        struct {
+                /**
+                 * @bar2.barbar: Description for @barbar inside @foo.bar2
+                 */
+                int barbar;
+        } bar2;
+  };
 
 Typedef documentation
 ---------------------