added Dataframes Tutorials

Author: mahmoudparsian

code/bonus_chapters/dataframes/README.md

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+Spark DataFrames Tutorial
+
+[1. DataFrames Tutorial: from Python Collections](./dataframe_tutorial_from_collection.py.md)
+
+[2. DataFrames Tutorial: from CSV Text Files](./dataframe_tutorial_from_text_files.py.md)
+
+[3. Arrays in DataFrames](./arrays_in_dataframes/)
+
+[4. Exploding Arrays in DataFrames](./explode_arrays_into_rows/)
+