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Most of the content was already covered in README.md. The remaining
content has been merged into the main readme file.

R=mpearson

Bug: none
Change-Id: I80d327189f17143f403af789001d5fb185d62e9e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2414683
Commit-Queue: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Auto-Submit: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809109}