Docs: move TW process info to handbook
https://docs.gitlab.com/ee/development/documentation/ and https://docs.gitlab.com/ee/development/documentation/workflow.html contain information about the Technical Writing team's process that should move to https://about.gitlab.com/handbook/engineering/ux/technical-writing/workflow/ (per @mikelewis pointing us to https://about.gitlab.com/handbook/git-page-update/#where-should-content-go after a discussion between me and @williamchia):
We need to look at migrating out info that's exclusive to how GitLab team members operate while still keeping content in docs that could be useful to contributors from the wider community.
Raising an issue first, so I can tie the two required MRs together - one for the www-gitlab-com
repo and the other for the gitlab
repo.