update the contributing guide

Author: jstourac

CONTRIBUTING.md

@@ -56,3 +56,8 @@ Pull requests are the best way to propose changes to the notebooks repository:
 ### Testing your PR locally
 
 - Test the changes locally, by manually running the `$make jupyter-${NOTEBOOK_NAME}-ubi8-python-3.8` from the terminal. This definitely helps in that initial phase.
+
+### Review and Merge Process
+
+- Once the PR is submitted, you can either select specific reviewers or let the bot to select reviewers [automatically](https://prow.ci.openshift.org/plugins?repo=opendatahub-io%2Fnotebooks).
+- For the PR to be merged, it must receive 2 reviews from the repository [approvals/reviewers](/OWNERS). Following that, an `/approve` comment must be added by someone with approval rights. If the author of the PR has approval rights, it is preferred that they perform the merge action.