Closes https://gitlab.com/gitlab-com/www-gitlab-com/issues/680 and #666 (closed) and #679 (closed)
Adding Kramdown (magic) guide to our Handbook/Marketing/Dev-Rel/Tech-Writing/ to facilitate writing content for GitLab's website and blog.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Closes https://gitlab.com/gitlab-com/www-gitlab-com/issues/680 and #666 (closed) and #679 (closed)
Adding Kramdown (magic) guide to our Handbook/Marketing/Dev-Rel/Tech-Writing/ to facilitate writing content for GitLab's website and blog.