DOC: Boolean Array Is Experimental
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [ ] whatsnew entry

BooleanArray and BooleanDtype are marked experimental, but its not marked as experimental in the user guide.
thanks @lithomas1  @meeseeksdev backport 1.3.x Something went wrong ... Please have  a look at my logs.