Add details for the first proof reader request

What does this MR do?

Add new details on how the first proofreader request will be evaluated when no one at GitLab (or Core Team) speaks the language. (Replaces https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26674/)

What are the relevant issue numbers?

N/A

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer