Add section on translation

Why is this change being made?

Localization of GitLab and the docs come up fairly frequently in technical writer candidate interview questions, and occasionally in questions to the #docs slack channel (example). I thought it would be helpful to have a short statement in our Technical Writing handbook pages that clarifies that:

• Translating GitLab the product is a community effort
• Translating product documentation on docs.gitlab.com is not part of the community effort, and not currently planned.

Author Checklist

• Provided a concise title for this Merge Request (MR)
• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
  • Copy/paste the Slack conversation to document it for later, or upload screenshots. Verify that no confidential data is added.
• Assign reviewers for this MR to the correct Directly Responsible Individual/s (DRI)
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the Maintained by section on the page being edited
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies
• If the changes affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.

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