Update CONTRIBUTING.md

Author: OriolAbril

CONTRIBUTING.md

@@ -21,13 +21,14 @@ These issue tickets are placed on one of the columns in this project based on th
 * **General updates:** notebooks in this column have pymc3 code up to date with v3, but don't use ArviZ (or do so only partially)
 * **ArviZ:** notebooks in this column use ArviZ but still have bad examples of pymc3 usage.
 * **Best practices:** notebooks in this column use ArviZ and pymc3 best practices. This column alone does not represent any extra updates, it is only the place for notebooks fulfilling the requirements to be in both "general updates" and "ArviZ".
-* **v4:** notebooks in this column use ArviZ and have been updated and executed with pymc3 v4.
+* **v4 (auto):** notebooks in this column have been updated and executed with pymc v4 using the `scripts/rerun.py` script, but they might not follow v4 best practices nor comply with the style guide
+* **Done:** notebooks in this column have been executed with v4, had their code updated to v4 best practices (there are now many things that were not possible before!) and also compy with the [style guide](https://docs.pymc.io/en/latest/contributing/jupyter_style.html)
 
 Therefore, all notebooks will be progressively updated along this path:
 
 ```
          / --> General updates -- \
-To Do --<                          >--> Best Practices --> v4
+To Do --<                          >--> Best Practices --> v4 (auto) --> Done
          \ -->      ArviZ      -- /
 ```