Update frequency code to address FutureWarning in processing.py

Fix: Update frequency code to address FutureWarning in processing.py

The use of 'M' frequency is deprecated and will be removed in a future version of pandas. Updated the code to use 'ME' instead as recommended in the warning message.

Changes:
- Updated the frequency code in processing.py from 'M' to 'ME' to ensure compatibility with future versions of pandas.

Reference:
- FutureWarning: 'M' is deprecated and will be removed in a future version, please use 'ME' instead.
/usr/local/lib/python3.10/dist-packages/utilsforecast/processing.py:428

README.md

@@ -128,7 +128,7 @@ import pandas as pd
 
 forecast_df = tfm.forecast_on_df(
     inputs=input_df,
-    freq="M",  # monthly
+    freq="ME",  # monthly
     value_name="y",
     num_jobs=-1,
 )