progress: added zscore fit

lib/pt_trading/rolling_window_fit.py

@@ -11,6 +11,14 @@ from statsmodels.tsa.vector_ar.vecm import VECM, VECMResults
 NanoPerMin = 1e9
     
 class RollingFit(PairsTradingFitMethod):
+    ''' 
+    N O T E:
+    =========
+    - This class remains to be abstract
+    - The following methods are to be implemented in the subclass:
+        - create_trading_pair()
+    =========
+    '''
     def __init__(self) -> None:
         super().__init__()