docs(reth-bench): fix incorrect output flag in README (#20240)

Author: yongkangc

bin/reth-bench/README.md

@@ -143,5 +143,5 @@ To reproduce the benchmark, first re-set the node to the block that the benchmar
 - **RPC Configuration**: The RPC endpoints should be accessible and configured correctly, specifically the RPC endpoint must support `eth_getBlockByNumber` and support fetching full transactions. The benchmark will make one RPC query per block as fast as possible, so ensure the RPC endpoint does not rate limit or block requests after a certain volume.
 - **Reproducibility**: Ensure that the node is at the same state before attempting to retry a benchmark. The `new-payload-fcu` command specifically will commit to the database, so the node must be rolled back using `reth stage unwind` to reproducibly retry benchmarks.
 - **Profiling tools**: If you are collecting CPU profiles, tools like [`samply`](https://github.com/mstange/samply) and [`perf`](https://perf.wiki.kernel.org/index.php/Main_Page) can be useful for analyzing node performance.
-- **Benchmark Data**: `reth-bench` additionally contains a `--benchmark.output` flag, which will output gas used benchmarks across the benchmark range in CSV format. This may be useful for further data analysis.
+- **Benchmark Data**: `reth-bench` additionally contains a `--output` flag, which will output gas used benchmarks across the benchmark range in CSV format. This may be useful for further data analysis.
 - **Platform Information**: To ensure accurate and reproducible benchmarking, document the platform details, including hardware specifications, OS version, and any other relevant information before publishing any benchmarks.