Update README.md

Author: louie-tsai

hardware/priority_core_turbo/README.md

@@ -33,7 +33,8 @@ PCT relies on **two Intel Speed Select features**:
 intel-speed-select tool mentioned below is installed inside the docker image in the [environment build seciton](#1-build-the-environment)
 
 `intel-speed-select turbo-freq info -l <level>` may print the same `bucket-0`,
-`bucket-1`, and `bucket-2` SST-TF table under multiple `powerdomain-*` anchors.
+`bucket-1`, and `bucket-2` SST-TF table under multiple `powerdomain-*` anchors.  
+A powerdomain anchor is the representative CPU id where a packages's internal power domain starts.   
 
 For PCT **capacity**, this flow counts `bucket-0` **once per package/socket**: