tweaks

README.md

 # csst-echo
 
 Docker image for csst-echo pipeline.
+
+```shell
+docker run csst-echo python /pipeline/app/run.py '{"dag_run": "12345"}'
+```

app/run.py

@@ -21,5 +21,12 @@ p.info()
 
 
 # parse JSON message
+if len(sys.argv) == 2:
+    msg = sys.argv[1]
+else:
+    raise ValueError("sys.argv[1] is required")
+d = p.message.msg2dict(msg)
+
+print(f"Input message: {d}")
 p.pipeline_logger.info(f"sys.argv = {sys.argv}")
 exit(0)
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