Add references to docs covering testing in DevTools
Add references to docs covering testing in DevTools

Bug: none
Change-Id: I46e82b7c0aa22aa1539c6e6d61cc920309882ec0
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2739599
Reviewed-by: Yang Guo <1cf0af8245a3a17a632a2c73531392b0f9761c76@chromium.org>
Commit-Queue: Alex Rudenko <d8d88e7d7e77f69e23d1d1432231196fb8e02a62@chromium.org>

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