docs: update README for cdk flags command

[vivian12300]

This PR adds information about the cdk flags command to the README.

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.28%. Comparing base (17ebf86) to head (14500a7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #789      +/-   ##
==========================================
- Coverage   81.49%   81.28%   -0.21%     
==========================================
  Files          63       63              
  Lines        8602     8602              
  Branches     1036     1036              
==========================================
- Hits         7010     6992      -18     
- Misses       1562     1578      +16     
- Partials       30       32       +2     

Flag	Coverage Δ
suite.unit	81.28% <ø> (-0.21%)	⬇️

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