Add documentation for Upset plots

[jenellewallace]

I am trying to upload a table to make an Upset plot, but getting the error:
Import Error
The provided data is in an incompatible form for visualization with Upset. To visualize this dataset, please upload set-based data or, if compatible, select columns to one-hot encode.

Please add documentation for this - under File Formats, the Upset section is blank.
Thank you!