update readme (#232)

Summary:
Pull Request resolved: #232

as title

Reviewed By: excelle08

Differential Revision: D83095155

fbshipit-source-id: 2046b9cd6a136f278354997913975156627ee882

Author: YifanYuan3

perfutils/README.md

@@ -24,3 +24,7 @@ collect_amd_zen4_perf_counters.sh
 ## ARM (Other)
 
 Use [topdown tool](https://learn.arm.com/install-guides/topdown-tool/).
+
+
+## Note
+When working with AMD Zen5-based CPUs, the `generate_amd_perf_report.py` has to also run on the same CPU; while for other architectures, the `generate_[cpu]_report.py` can be run on any machine.