Point to the test documentation from the workflow script

This adds one comment line to o2dpg_sim_workflow.py so the CVMFS-based
simulation tests can be exercised on a pull request.

- The change is a comment only and alters no behaviour.
- Touching MC/bin is what makes the workflow tests run, which is the point.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: sawenzel

MC/bin/o2dpg_sim_workflow.py

@@ -5,6 +5,7 @@
 # It aims to handle the different MC possible configurations
 # It just creates a workflow.json txt file, to execute the workflow one must execute right after
 #   ${O2DPG_ROOT}/MC/bin/o2_dpg_workflow_runner.py -f workflow.json
+# The tests covering this script are described in test/README.md.
 #
 # Execution examples:
 #  - pp PYTHIA jets, 2 events, triggered on high pT decay photons on all barrel calorimeters acceptance, eCMS 13 TeV