README utilization example uses --processes, but the command defines --workers

Noted while adding the *Queues* section to the README (fair multi-queue scheduling, `codingjoe-fair-multi-queue-scheduling`).

The README's *Utilization* section advertises:

```console
uv run manage.py threadmill worker --processes 4 --threads 2
```

but `WorkerCommand.add_arguments()` defines `-w`/`--workers`, not `--processes`. The example fails with an unrecognised-argument error.

Fix is to rename the flag in the README example (or add an alias, if `--processes` is the intended name).

Open the README's Utilization section and compare its worker command example with WorkerCommand.add_arguments(), which defines the available flags. Update the example so it uses the intended option, then verify that the documented command no longer produces an unrecognised-argument error.

Written by the indexing model from the issue text.