Add missing step in usage (Baldinof/roadrunner-bundle#117)

[sweoggy]

Since 2023.X release, the binary download utility is no longer automatically included in RoadRunner.

I put this as a suggestion in composer.json rather than a requirement, as there are different options of getting RoadRunner, this being one of the most convenient ones, at least for local development.

[Baldinof]

Thank you!