Update an absolute same-site link URL on the Handbook Usage page.
This makes the "Handbook Changelog" link URL root-relative at https://about.gitlab.com/handbook/handbook-usage/#how-to-change-or-define-a-process.
This makes the "Handbook Changelog" link URL root-relative at https://about.gitlab.com/handbook/handbook-usage/#how-to-change-or-define-a-process.