Added documentation on perf waterfall.

docs/speed/perf_waterfall.md

Index: docs/speed/perf_waterfall.md
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+# chromium.perf Waterfall
+
+## Overview
+
+The [chromium.perf waterfall](http://build.chromium.org/p/chromium.perf/waterfall)
+continuously builds and runs our performance tests on real Android, Windows,
+Mac, and Linux hardware. Results are reported to the
+[Performance Dashboard](https://chromeperf.appspot.com/) for analysis. The
+[Perfbot Health Sheriffing Rotation](perf_bot_sheriffing.md) keeps the build
+green and files bugs on regressions. They maintain
+[Chrome's Core Principles](https://www.chromium.org/developers/core-principles)
+of speed:
+
+> "If you make a change that regresses measured performance, you will be
+> required to fix it or revert".
+
+## Contact
+
+  * You can reach the Chromium performance sheriffs at perf-sheriffs@chromium.org.
+  * Bugs on waterfall issues should have Component:
+    [Speed>Benchmarks>Waterfall](https://bugs.chromium.org/p/chromium/issues/list?can=2&q=component%3ASpeed%3EBenchmarks%3EWaterfall+&colspec=ID+Pri+M+Stars+ReleaseBlock+Component+Status+Owner+Summary+OS+Modified&x=m&y=releaseblock&cells=ids).
+
+## Links
+
+  * [Perfbot Health Sheriffing Rotation](perf_bot_sheriffing.md)
+  * [Debugging an Android Perf Failure](perf_bot_sheriffing.md#Android-Device-failures)
+  * TODO: Page on how to repro failures locally
+  * TODO: Page on how to connect to bot in lab
+  * TODO: Page on how to hack on buildbot/recipe code
+  * TODO: Page on bringing up new hardware