Add documentation about shortlist of benchmarks to run for evaluting perf change

Change-Id: I7251d6d06c993d241233e27b59ca598594a322a9

NOTRY=true # documentation change CL

Change-Id: I7251d6d06c993d241233e27b59ca598594a322a9
Reviewed-on: https://chromium-review.googlesource.com/990590
Commit-Queue: Ned Nguyen <nednguyen@google.com>
Reviewed-by: Annie Sullivan <sullivan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547502}

docs/speed/benchmark/benchmark_short_list.md

+# Chrome Speed Benchmark Shortlist
+
+Target audience: if you are a Chrome developer who wants to quickly gauge how
+your change would affect Chrome performance, then this doc is for you.
+
+> **Warning:** this doc just gives you a general reduced list of Chrome
+> benchmarks to try out if you don’t know where to start or just want some quick
+> feedback. There is no guarantee that if your change doesn’t regress these
+> benchmarks, it won’t regress any benchmarks or regress UMA metrics. We believe
+> it’s best to rely on [key UMA metrics](https://docs.google.com/document/d/1Ww487ZskJ-xBmJGwPO-XPz_QcJvw-kSNffm0nPhVpj8/edit#heading=h.2uunmi119swk)
+> to evaluate performance effects of any Chrome change.
+
+Here is the list of benchmarks which we recommend:
+Android:
+*   system_health.common_mobile
+*   system_health.memory_mobile
+*   experimental.startup.android.coldish
+
+Desktop:
+*   system_health.common_desktop
+*   system_health.memory_desktop
+
+Both desktop & mobile:
+*   speedometer2
+
+
+Instructions for how to run these benchmarks:
+*   [Running them locally](https://github.com/catapult-project/catapult/blob/master/telemetry/docs/run_benchmarks_locally.md)
+*   [Running on perf trybot](https://chromium.googlesource.com/chromium/src/+/master/docs/speed/perf_trybots.md)