feat: Ch03 Ergodic Processes

Change-Id: Ic73be4a8ed8afd2e7d181536fd9d420c75f0781f
diff --git a/dcs/frames/groups.py b/dcs/frames/groups.py
index 4ad16f4..a7e2f4d 100644
--- a/dcs/frames/groups.py
+++ b/dcs/frames/groups.py
@@ -9,3 +9,7 @@
 
 class Ch02Group(Group):
     NAME = 'Chapter 02'
+
+
+class Ch03Group(Group):
+    NAME = 'Chapter 03'