DOC: add "experimental" warning to some new array-related features?
I would propose to add some "experimental" warnings in certain docstrings / parts of the whatsnew for the new array-related functionality we are adding in 0.24.0. Thoughts about that?

And if we do that, where should we add it? I was thinking about `IntegerArray`, `pd.array`, `PandasArray`, maybe `.array` attribute