Missing documentation of the meaning of errorbars in cat_plot

Greetings!

When using cat_plot, I failed to understand the meaning of the errorbars. Depending on the field (mine is psychology) it might not be obvious what errorbars should represent (SE, SD, 95% CI, 99% CI, ...). Even from looking into the function's code it is not obvious how the errorbars are computed. It would be very useful to have a comment on that in the package documentation.

Start by locating the cat_plot documentation and the function implementation referenced in the issue. Read how the errorbars are computed, then document which quantity they represent and add the explanation to the package documentation; done means users can distinguish the errorbars from SE, SD, and confidence intervals.

Written by the indexing model from the issue text.