Link to groupby issues

Author: TomNicholas

README.md

@@ -43,9 +43,10 @@ Some things almost certainly won't work yet:
 - Certain operations called in xarray but not implemented in cubed, for instance `pad` (see https://github.com/tomwhite/cubed/issues/193)
 - Array operations involving NaNs - for now use `skipna=True` to avoid eager loading (see https://github.com/pydata/xarray/issues/7243)
 - Using `parallel=True` with `xr.open_mfdataset` won't work because cubed doesn't implement a version of `dask.Delayed` (see https://github.com/pydata/xarray/issues/7810)
+- Groupby (see https://github.com/tomwhite/cubed/issues/223 and https://github.com/xarray-contrib/flox/issues/224)
 
 and some other things _might_ work but have not yet been tried:
-- Groupby
+
 - Saving to formats other than zarr
 
 In general a bug could take the form of an error, or of a silent attempt to coerce the array type to numpy by immediately computing the underlying array.