ci/ci_run_n_monitor: add docs for multiple targets

clarify how multiple targets can be used with the pipe character.

Signed-off-by: Helen Koike <helen.koike@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25472>

bin/ci/ci_run_n_monitor.py

@@ -238,7 +238,11 @@ def parse_args() -> None:
         epilog="Example: mesa-monitor.py --rev $(git rev-parse HEAD) "
         + '--target ".*traces" ',
     )
-    parser.add_argument("--target", metavar="target-job", help="Target job")
+    parser.add_argument(
+        "--target",
+        metavar="target-job",
+        help="Target job regex. For multiple targets, separate with pipe | character",
+    )
     parser.add_argument(
         "--token",
         metavar="token",