docs: Documentation update

Change-Id: I6f916eb822a59e980e8fb1134886c3431755119c
diff --git a/model/ndn-global-router.hpp b/model/ndn-global-router.hpp
index 76eb8f8..4713a5b 100644
--- a/model/ndn-global-router.hpp
+++ b/model/ndn-global-router.hpp
@@ -38,7 +38,7 @@
 class L3Protocol;
 
 /**
- * @ingroup ndn
+ * @ingroup ndn-helpers
  * @brief Class representing global router interface for ndnSIM
  */
 class GlobalRouter : public Object {