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Update README and one-pager for the latest pattern histogram
instructions. Reuse/Remove some of the legacy histogram-suffixes docs.

Change-Id: I0bc63ea8d419c5ab861d5d64f39ecc150c6ad8b0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2380344
Commit-Queue: Weilun Shi <sweilun@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Auto-Submit: Weilun Shi <sweilun@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803603}