Add xr.open_dataset("file.tif", engine="rasterio") to docs

[raybellwaves]

Kind of related to #4697

I see https://corteva.github.io/rioxarray/stable/getting_started/getting_started.html#rioxarray

shows

ds = xarray.open_dataset("file.tif", engine="rasterio")

This could be added to

https://xarray.pydata.org/en/latest/user-guide/io.html#rasterio

[sjvrijn]

The link to corteva has been added to the rasterio user guide in #5808, so I think this issue can be closed too.