Update quantization related section in readme

Summary: Updated the command since python_binary doesnt work with oss buck2

Reviewed By: larryliu0820

Differential Revision: D48357047

fbshipit-source-id: 7c9376f1fc14d4d5144cffc28ad58d98e338dadd

Author: kimishpatel

examples/README.md

@@ -59,7 +59,7 @@ Here is the [Quantization Flow Docs](/docs/website/docs/tutorials/quantization_f
 
 You can run quantization test with the following command:
 ```bash
-buck2 run executorch/examples/quantization:example -- --model_name="mv2" # for MobileNetv2
+python3 -m examples.quantization.example --model_name "mv2" # for MobileNetv2
 ```
 It will print both the original model after capture and quantized model.