Added github-handle for Khanh Cao in design-systems.md

[patelbansi3009]

Fixes #6701

What changes did you make?

• Added github-handle for Khanh Cao in design-systems.md.

Why did you make the changes (we will use this info to test)?

• To Reduce redundancy in the project data.

Screenshots of Proposed Changes Of The Website (if any, please do not screen shot code changes)

• Adding a line of code. No visual changes to the website.

[github-actions[bot]]

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git checkout -b patelbansi3009-add-github-handle-Khanh-Cao-6701 gh-pages
git pull https://github.com/patelbansi3009/website.git add-github-handle-Khanh-Cao-6701

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https://github.com/patelbansi3009/website/blob/add-github-handle-Khanh-Cao-6701/CONTRIBUTING.md  

[jchue]

Availability: May 1, after 5 PM PDT ETA: May 1