Update design review guidelines
Update design review guidelines

TBR=Shane.Clifford@microsoft.com, leolee@microsoft.com

Change-Id: Iec959032ceb21ef08422dd06d534556e2c5765aa
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2067060
Reviewed-by: Yang Guo <1cf0af8245a3a17a632a2c73531392b0f9761c76@chromium.org>
Commit-Queue: Yang Guo <1cf0af8245a3a17a632a2c73531392b0f9761c76@chromium.org>

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