Figure out how to add demographic information to GDC head-and-mouth data

[gaurav]

The GDC import doesn't include demographic information. We should modify the import at https://github.com/cancerDHC/example-data/blob/main/head-and-mouth/Head%20and%20Mouth%20Cancer%20Datasets.ipynb to include this information.

Related to #6.

[gaurav]

I have a suspicion that this might be as easy as modifying "expand": "diagnoses,samples" to "expand": "diagnoses,samples,demographic", but it probably isn't that easy :)

[jooho-lee-kim]

It was easy like that.
Do we want to update gdc-head-and-mouth.json file to include demographic portion of data?

[gaurav]

Yes, please!