Support pyspark.sql.Dataframe in TFDataset (#1983)
Support pyspark.sql.Dataframe in TFDataset (#1983)

* support pyspark.sql.Dataframe in TFDataset

* add document

yangw1234/BigDL,yangw1234/BigDL,yangw1234/BigDL,intel-analytics/BigDL,intel-analytics/BigDL,intel-analytics/BigDL,yangw1234/BigDL,intel-analytics/BigDL