Clarify UI text and documentation labeling

Add a new bullet to Partnering with Technical Writers to clarify that the documentation label is required if UI text changes might impact documentation steps. Example: Update the "menu" menu to be a simpler, less redundant and straightfoward

Why is this change being made?

This change helps raise awareness that the documentation label should be considered when a UI text change is in the works.

Related handbook links that are already referenced show Technical Writing involvement in:

• Validation/Design phase
• Build phase

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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