docs: interactive rebase tutorial link

[petermetz]

Description

The CONTRIBUTING.md file should have a link to this excellent article as part of a recommended reading list of git resources:
https://about.gitlab.com/blog/2020/11/23/keep-git-history-clean-with-interactive-rebase/

Acceptance Criteria

1. Just make sure there's a link to the article in the documentation, preferably somewhere early on so that people who are just starting out can find it before diving deep into the rest of the git stuff which can be very daunting at first.

cc: @takeutak @sfuji822 @hartm @jonathan-m-hamilton @AzaharaC @jordigiam @kikoncuo