Fix broken links to point to https://about.gitlab.com/handbook instead of http://localhost

Noticed a couple of links pointing to localhost.

The git-page-update page says

"All internal links (links leading to other parts of the website) should be relative."

but the working links seemed absolute, so the same pattern is maintained.

(Note: There is one attempt at a relative URL, production/#workflow--how-we-work, but even that is broken since production is one level above teams)