notebooks/build_person_directory.ipynb will fail after the step of `### Adding and associating a new face`

[yungshinlintw]

When running notebooks/build_person_directory.ipynb, it will fail after the step of ### Adding and associating a new face.

This is because that the code will need to be updated with real data. This is not ideal as an example.

By comparison, C# version of the sample has been improved with sample data:

Azure-Samples/azure-ai-content-understanding-dotnet#5

We should fix the Python sample by following the .NET improvement too.

[changjian-wang]

PR for improving Build Person Directory