Add documentation.

Author: Ghislain Fourny

README.md

@@ -341,6 +341,9 @@ Even more queries can be found [here](https://colab.research.google.com/github/R
 ## Version 2.0.0
 - Aligned on the brand new RumbleDB 2.0 release.
 - Improved display of pandas dataframes output with -pdf in Jupyter notebooks.
+- if error info is activated in the configuration, then they are now printed in the notebook.
+- JSON nulls are now by default conflated with absent upon validating for dataframe output, this can be deactivated in the configuration.
+- The materialization error upon df/pdf output is now fixed.
 
 ## Version 2.0.0 alpha 1
 - When returning a single-column DataFrame with atomic values, the name is now __value and not value to avoid collisions with user-defined columns.