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This adds some basic documentation laying out what the project is, how
to use it, and the MVP bots. It is intended as a user guide rather than
technical details.

Bug: None
Change-Id: I7d90f542d2aeb33eecfd836693f2741ad91588c6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2451505
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Reviewed-by: Luke Z <lpz@chromium.org>
Reviewed-by: Robert Ma <robertma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814646}