What's Changed
`method=None` by default, and we have [heuristics](https://flox.readthedocs.io/en/latest/implementation.html#heuristics) for setting it appropriately!
* Heuristics for auto-guessing `"method"` by dcherian in https://github.com/xarray-contrib/flox/pull/314
* Optimize bitmask finding some more. by dcherian in https://github.com/xarray-contrib/flox/pull/326
* Add docs on `method=None` heuristics by dcherian in https://github.com/xarray-contrib/flox/pull/328
**Full Changelog**: https://github.com/xarray-contrib/flox/compare/v0.8.9...v0.9.0