Adding XC model tutorial

[advikavs]

Description

Fix #(issue)

Type of change

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
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Checklist

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  • Run yapf -i <modified file> and check no errors (yapf version must be 0.32.0)
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[rbharath]

Tutorial is almost ready to merge. A couple of small changes needed

[rbharath]

LGTM