Add guidance for non-SUS label usage

Why is this change being made?

This MR adds additional clarification to the UI text label usage for TWs to indicate when the non-SUS label should or shouldn't be used.

The MR also updates the line wrapping for a couple of lines in the section, to match expected practices for Handbook-related pages.

Author Checklist

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• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
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