DOC: add pandas.DataFrame.to_xarray (#3994)

Co-authored-by: Ray Bell <rayjognbell0@gmail.com>

Author: raybellwaves

xarray/core/dataset.py

@@ -4598,6 +4598,7 @@ def from_dataframe(cls, dataframe: pd.DataFrame, sparse: bool = False) -> "Datas
         See also
         --------
         xarray.DataArray.from_series
+        pandas.DataFrame.to_xarray
         """
         # TODO: Add an option to remove dimensions along which the variables
         # are constant, to enable consistent serialization to/from a dataframe,