docs: clarify design tokens requirements in brand example README

[brian-smith-tcril]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.17%. Comparing base (4ce8bad) to head (2c653e2).

Additional details and impacted files

@@           Coverage Diff           @@
##             main       #7   +/-   ##
=======================================
  Coverage   88.17%   88.17%           
=======================================
  Files          12       12           
  Lines         406      406           
  Branches       16       16           
=======================================
  Hits          358      358           
  Misses         40       40           
  Partials        8        8           

Flag	Coverage Δ
unittests	88.17% <ø> (ø)

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