fix: example/build_file_generation/README.md (#1164)

This PR updates outdated README.md of example.

Closes #1160

---------

Signed-off-by: Thulio Ferraz Assis <[email protected]>
Co-authored-by: Thulio Ferraz Assis <[email protected]>

Author: ofey404

examples/build_file_generation/README.md

@@ -5,7 +5,9 @@ extension, so that targets like `py_library` and `py_binary` can be
 automatically created just by running
 
 ```sh
-$ bazel run //:gazelle
+bazel run //:requirements.update
+bazel run //:gazelle_python_manifest.update
+bazel run //:gazelle
 ```
 
 As a demo, try creating a `__main__.py` file in this directory, then