Workaround for fbs file not found (#3855)

Summary: Pull Request resolved: #3855

Reviewed By: cccclai

Differential Revision: D58206698

Pulled By: kirklandsign

fbshipit-source-id: f5e70d38f39860e9ca4e8e1d0b4fd697445fdbe8

backends/qualcomm/setup.md

@@ -55,6 +55,13 @@ export LD_LIBRARY_PATH=$QNN_SDK_ROOT/lib/x86_64-linux-clang/:$LD_LIBRARY_PATH
 export PYTHONPATH=$EXECUTORCH_ROOT/..
 ```
 
+Note: Since we set `PYTHONPATH`, we may have issue with finding `program.fbs`
+and `scalar_type.fbs` when we export a model, because they are installed into
+`pip-out` directory with the same package name pattern. A workaround is that
+we copy `$EXECUTORCH_ROOT/pip-out/lib.linux-x86_64-cpython-310/executorch/exir/_serialize/program.fbs`
+and `$EXECUTORCH_ROOT/pip-out/lib.linux-x86_64-cpython-310/executorch/exir/_serialize/scalar_type.fbs`
+to `$EXECUTORCH_ROOT/exir/_serialize/`.
+
 
 ## End to End Inference