update toc

book/_toc.yml

@@ -191,11 +191,13 @@ parts:
         - file: time_series/exercise4.ipynb
       - file: time_series/arma
         title: "AutoRegressive Moving Average (ARMA) process"
-    # START REMOVE-FROM-PUBLISH
+        sections:
+        - file: time_series/exercise5.ipynb
       - file: time_series/forecasting
         title: "Time Series forecasting"
       - file: time_series/optional
         title: "Supplementary material"
+    # START REMOVE-FROM-PUBLISH        
       - file: time_series/notebook
         title: Notebook
     - file: optimization/overview