GC: update comment in MarkingDelegate::scanRoots()

Signed-off-by: Jan Vrany <jan.vrany@fit.cvut.cz>

example/glue/MarkingDelegate.hpp

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2017, 2020 IBM Corp. and others
+ * Copyright (c) 2017, 2021 IBM Corp. and others
  *
  * This program and the accompanying materials are made available under
  * the terms of the Eclipse Public License 2.0 which accompanies this
@@ -150,7 +150,9 @@ class MM_MarkingDelegate
 	 * that would not be discovered in the subsequent traversal of the object reference graph depending from the
 	 * root set.
 	 *
-	 * For each root object identified, MM_MarkingScheme::scanObject() must be called via _markingScheme.
+	 * For each root object identified, MM_MarkingScheme::markObject() must be called via _markingScheme.
+	 * MM_MarkingScheme::markObject() besides marking the object as live (if already not marked by another root)
+	 * pushes the object onto the working stack for further scanning.
 	 *
 	 * @param env The environment for the calling thread
 	 */