resources, gpu-compute: update HACC README

Update HACC README to reflect changes to compile and run correctly
with ROCm 4.

Change-Id: I9b420ee5dbb3600c93e1d1dfe73e8ca33d1f71d4
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-resources/+/50988
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby R. Bruce <bbruce@ucdavis.edu>
diff --git a/src/gpu/halo-finder/README.md b/src/gpu/halo-finder/README.md
index 9bf123c..e52b069 100644
--- a/src/gpu/halo-finder/README.md
+++ b/src/gpu/halo-finder/README.md
@@ -34,7 +34,7 @@
 
 To build the Docker image and the benchmark:
 
-Note: HACC requires a number of environment variables to be set to compile and run correctly.  Our Dockerfile sets these flags appropriately for you.  This Dockerfile automatically runs when a new docker image is created, which is why our instructions below recommend doing this.  If you would prefer not doing this, then you will need to pass in these environment variables using -e.
+Note: HACC requires a number of environment variables to be set to compile and run correctly.  Our Dockerfile sets these flags appropriately for you.  This Dockerfile automatically runs when a new docker image is created, including building for both gfx801 and gfx803, which is why our instructions below recommend doing this.  If you would prefer not doing this, then you will need to pass in these environment variables using -e.
 
 ```
 cd src/gpu/halo-finder