explain that 'stack' barmode also works for px.bar

[Ddedalus]

Hi, this is my first pull request, if I choose the wrong branch, please let me know :)

Just a small extension to the available options of px.bar to begin with.

[nicolaskruchten]

Thanks for this PR! I had initially left out "stack" because it's so easy to misunderstand what it does with respect to negative values... We probably should indeed add it but with a clear warning about how unintuitive the output can be.

[Ddedalus]

I've tried it out on a small example and added a brief note. If you think more explanation is needed there (or my understanding is wrong), please go ahead. It may be a good idea to put a longer description in go.Bar docs as well...

Out of curiosity, how would you create a stack plot where positive and negative values are stacked separately on the opposite sides of the x-axis?

[emmanuelle]

Thanks for updating the PR @Ddedalus ! @nicolaskruchten I think we can merge this one?

[nicolaskruchten]

Right, so to stack above and below zero the option is “relative”. The “stack” option is supported but needs a clear and scary warning like “this is almost never what you want to use and will often mislead viewers when negative values are involved” or something like that. We have to support it for backwards compatibility reasons but IMO it’s quite a dangerous option.