Document feature differences between object formats

[wish1832]

Add documentation explaining features that don't work in either of the three object formats. For example, SingleCellExperiment objects don't support subsetting based on feature expression, or differential gene expresssion, and it is not high priority to add these capabilities before release.

We should also say that AUC values won't be shown for Seurat v5 or anndata objects.

[jairav]

@wish1832 will generate table, @agillen will summarize for documentation