[tools/onnx-subgraph] add guide in README.md for subgraphs verification (#14821)

guide for mse comparing of src model and multi sub models

ONE-DCO-1.0-Signed-off-by: Youxin Chen <[email protected]>

Author: chenyx113

tools/onnx_subgraph/README.md

@@ -60,3 +60,18 @@ sub models.
     ├── NPUsubgraph0.onnx
     └── NPUsubgraph1.onnx
 ```
+## Verify the subgraphs inference with original model file
+compare the MSE of original inference result and subgraphs inference result
+```bash
+    python scripts/single_vs_multiple_onnx.py \
+           -s ./resnet-test.onnx \
+           -m ./subgraphs/ \
+           -n scripts/subgraphs_ios.txt
+```
+output:
+```bash
+    Single model inference completed!
+    Multiple subgraph inference completed!
+    Comparing inference results between single ONNX model and multiple subgraphs...
+    Output '316' MSE: 5.125894080395578e-14
+```