add extra document comment

Signed-off-by: Chen Lihui <lihui.chen@sony.com>

include/class_loader/class_loader_core.hpp

@@ -91,6 +91,9 @@ class MetaObjectGraveyardVector : public MetaObjectVector
     // when destroying `meta_object` in the unique_ptr deleter. Because the static variable in
     // `getMetaObjectGraveyard()` could be finalized before the static variable
     // `g_register_plugin_ ## UniqueID` in some circumstances.
+    // NOTE of vector dctor in the STL: `note that if the elements themselves are pointers, the
+    // pointed-to memory is not touched in any way.  Managing the pointer is the user's
+    // responsibility.`
     clear();
   }
 };