ci_run_n_monitor: add comment to explain "MR > fork" logic

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25186>

bin/ci/ci_run_n_monitor.py

@@ -317,9 +317,11 @@ if __name__ == "__main__":
         else:
             if not REV:
                 REV = check_output(['git', 'rev-parse', 'HEAD']).decode('ascii').strip()
+            # Look for an MR pipeline first
             cur_project = gl.projects.get("mesa/mesa")
             pipe = wait_for_pipeline(cur_project, REV, timeout=10)
             if not pipe:
+                # Fallback to a pipeline in the user's fork
                 cur_project = get_gitlab_project(gl, args.project)
                 pipe = wait_for_pipeline(cur_project, REV)