more docstring

speechx/examples/ds2_ol/onnx/README.md

+# DeepSpeech2 ONNX model
+
+1. convert ds2 model to ONNX, using Paddle2ONNX.
+2. check paddleinference and onnxruntime output equal.
+
+## Using
+
+```
+bash run.sh
+```
+
+## Outputs
+∂∂∂
+```
+ls exp/model.onnx∂∂∂
+```
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