test/orfs: add RULES_JSON update note in README.md

Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

Author: oharboe

test/orfs/README.md

@@ -4,6 +4,11 @@ A set of ORFS integration tests that runs in a few minutes suitable for inclusio
 
     bazel -c opt test ...
 
+## Updating RULES_JSON files
+
+1. Run `bazel run -c opt //test/orfs/gcd:gcd_update` to update RULES_JSON file for a design. This will build and run OpenROAD to generate a new RULES_JSON file and update the RULES_JSON source file.
+2. Create commit for RULES_JSON file
+
 ## Updating ORFS and bazel-orfs
 
 `bazel run @bazel-orfs//:bump`, this will find the latest bazel-orfs and ORFS docker image and update MODULE.bazel and MODULE.bazel.lock.