Update docs for benchmarks.

packages/flutter/benchmark/README.md

@@ -7,12 +7,16 @@ so benchmarks here are typically run by hand. To run a benchmark:
 1. Build `sky_shell` for Linux Release using the instructions in the
    [Engine repository](https://github.com/flutter/engine).
 
-2. Run `pub get` in the `packages/unit` directory.
+2. Run `pub get` in the `packages/flutter` directory.
 
 3. Run the benchmarks by running the following command from the root
-   of the flutter repository (replacing `stocks/layout_bench.dart`
-   with the path to whichever benchmark you want to run):
+   of the flutter repository. Replace `stocks/layout_bench.dart` with
+   the path to whichever benchmark you want to run. If you didn't
+   build the engine in the recommended place, then also update the
+   path accordingly. If you made changes to sky_services, you'll also
+   need to update the `pubspec.yaml` file to point to that using a
+   dependency_override.
 
 ```
-/path/to/engine/src/out/Release/sky_shell packages/unit/benchmark/stocks/layout_bench.dart --package-root=packages/unit/packages
+../engine/src/out/Release/sky_shell packages/flutter/benchmark/stocks/layout_bench.dart --package-root=packages/flutter/packages
 ```

packages/flutter/pubspec.yaml

@@ -26,7 +26,7 @@ dependencies:
 dev_dependencies:
   flutter_test:
     path: ../flutter_test
-  stocks:
+  stocks: # for the benchmarks
     path: ../../examples/stocks
 
 environment: