Add CodSpeed badge to benchmark.md

Added CodSpeed badge to benchmarking documentation.

Author: shenxianpeng

docs/benchmark.md

@@ -1,5 +1,7 @@
 # Benchmarking
 
+[![CodSpeed Badge](https://img.shields.io/endpoint?url=https://codspeed.io/badge.json)](https://codspeed.io/cpp-linter/cpp-linter-hooks)
+
 This document outlines the benchmarking process for comparing the performance of cpp-linter-hooks and mirrors-clang-format.
 
 ## Running the Benchmark