[Doc] Add python kernel sample data guide.

[yoyo-wu98]

Since we have added the Python Kernel of the open-digger and there is an issue #968 asking for it, the guide of the Sample Data Usage with Python Kernel should be added.

[frank-zsy]

My concern is that right now we add kernel related docs into sample_data readme, but actually the sample data doc should not be mixed with kernel doc at all because they are totally different thing here.

Can we split the kernel related docs into another place and only reference in the sample data doc?

[frank-zsy]

I think we can merge this PR now and consider how to improve the docs later.

Thanks for the contribution @yoyo-wu98

/approve

[yoyo-wu98]

Many thx:)