Fix links that 404 and style changes

What does this MR do?

Fixes the 404ing links in one file.

Makes file also confirm to suggested proselint and markdownlint rules.

Related issues

Relates to: https://gitlab.com/gitlab-org/gitlab-ce/issues/51696.

Author's checklist

• Apply the correct labels and milestone
• Crosslink the document from the higher-level index
• Crosslink the document from other subject-related docs
• Correctly apply the product badges and tiers
• Port the MR to EE (or backport from CE): always recommended, required when the ee-compat-check job fails

Review checklist

• Your team's review (required)
• PM's review (recommended, but not a blocker)
• Technical writer's review (required)
• Merge the EE-MR first, CE-MR afterwards