docs(readme): reflink limitation

Author: KSXGitHub

README.md

@@ -59,6 +59,7 @@ The benchmark was generated by [a GitHub Workflow](https://github.com/KSXGitHub/
 
 ## Limitations
 
+* Ignorant of reflinks (from COW filesystems such as btrfs and zfs).
 * Do not follow symbolic links.
 * Do not differentiate filesystem: Mounted folders are counted as normal folders.
 * The runtime is optimized at the expense of binary size.