docs(readme): add --deduplicate-hardlinks

Resolves #301

Author: KSXGitHub

README.md

@@ -29,6 +29,7 @@ The benchmark was generated by [a GitHub Workflow](https://github.com/KSXGitHub/
 
 <figure>
   <img src="https://ksxgithub.github.io/parallel-disk-usage-0.20.0-benchmarks/tmp.benchmark-report.competing.block-size.svg">
+  <img src="https://ksxgithub.github.io/parallel-disk-usage-0.20.0-benchmarks/tmp.benchmark-report.competing.deduplicate-hardlinks.svg">
   <figcaption align="center">
     benchmark results
     <em>(lower is better)</em>