Document the fact that bisect requires rooted Android device

This CL notes that on Android run_benchmark requires the device to be rooted.
This should be helpful to people attempting this for the first time. Motivated
by https://bugs.chromium.org/p/chromium/issues/detail?id=1026774#c11.

Change-Id: Ic3fa62ab60c882a4e8ef3f6328242f73c3a6d61e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1946455Reviewed-by: Annie Sullivan <sullivan@chromium.org>
Commit-Queue: Nicolás Peña Moreno <npm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#720998}

docs/speed/addressing_performance_regressions.md

@@ -90,7 +90,8 @@ making the regression more likely to reproduce. From the Pinpoint Job page,
 clicking the `+` button in the bottom-right corner to test a patch with the
 current configuration.
 
-You can also run locally:
+You can also run locally (note that running this successfully on Android
+requires the device to be rooted):
 ```
 src$ tools/perf/run_benchmark benchmark_name --story-filter story_name
 ```