Teach `mojo_benchmark` to upload results to perf dashboard.

mojo/devtools/common/docs/mojo_benchmark.md

 # mojo_benchmark
 
 `mojo_benchmark` allows you to run performance tests for any Mojo application
 that participates in the [tracing
 ecosystem](https://github.com/domokit/mojo/blob/master/mojo/services/tracing/interfaces/tracing.mojom)
 with no app changes required.
 
 The script reads a list of benchmarks to run from a file, runs each benchmark in
 controlled caching conditions with tracing enabled and performs specified
 measurements on the collected trace data.
@@ skipping 54 matching lines @@
   {
     'name': 'My app initialization',
     'app': 'https://my_domain/my_app.mojo',
     'duration': 10,
     'measurements': [
       'time_until/my_app/initialized',
     ],
   },
 ]
 ```
+
+## Dashboard
+
+`mojo_benchmark` supports uploading the results to an instance of a Catapult
+performance dashboard. In order to upload the results of a run to performance
+dashboard, pass the `--upload` flag along with required meta-data describing the
+data being uploaded:
+
+```sh
+mojo_benchmark \
+--upload \
+--master-name my-master \
+--bot-name my-bot \
+--test-name my-test-suite
+--builder-name my-builder \
+--build-number my-build
+--server-url http://my-server.example.com
+```
+
+If no `--server-url` is specified, the script assumes that a local instance of
+the dashboard is running at `http://localhost:8080`. The script assumes that the
+working directory from which it is called is a git repository and queries it to
+determine the sequential number identifying the revision (as the number of
+commits in the current branch in the repository).
+
+For more information refer to:
+
+ - [Catapult project](https://github.com/catapult-project/catapult)