doc string update

Author: jchanvfx

NodeGraphQt/nodes/group_node.py

@@ -10,6 +10,8 @@
 
 class GroupNode(BaseNode):
     """
+    `Implemented in` ``v0.2.0``
+
     The ``NodeGraphQt.GroupNode`` class extends from the
     :class:``NodeGraphQt.BaseNode`` class with the ability to nest other nodes
     inside of it.