Update links and descriptive text within Contracts.
This updates link text, link URLs, and nearby descriptive text within https://about.gitlab.com/handbook/contracts/.
- A "page" link now uses the title of the page to better describe it.
- Absolute same-site link URLs are now relative to the site root.
- A missing trailing slash has been added to skip HTTP redirects.
- "proccesses" has been changed to "processes"