Add more context to demo datasets

[fedarko]

Just a little thing that'd help clarify what this tool does. I think all of the demo datasets (both the 5 we have up now and the two that'd be added in #285) have corresponding Jupyter Notebooks or other analysis notes we can link to -- this would go a long way in clarifying where the "rankings" being used came from. This could even replace the Briefly: What was this study looking at? column entirely.

Would also be nice to have a direct link to Emperor DEICODE biplots where possible (e.g. sleep apnea and moving pictures), but that's not as important as just adding more context in general.

(Edit: we could even do away with the table entirely, and just give each demo dataset an arbitrary free-text paragraph/div/whatever to contain whatever relevant content we want. This could include arbitrary stuff -- e.g. Songbird formulas used, biplot links, paper links, arbitrarily long descriptions of the dataset, a quick explanation as to what Qurro is useful for for this dataset, ...)