add documentation how to read columns from parquet file

Author: hoffmann

doc/source/io.rst

@@ -4538,6 +4538,16 @@ Read from a parquet file.
 
    result.dtypes
 
+Read only certain columns of a parquet file. 
+
+.. ipython:: python
+
+   result = pd.read_parquet('example_pa.parquet', engine='pyarrow', columns=['a', 'b'])
+   result = pd.read_parquet('example_fp.parquet', engine='fastparquet', columns=['a', 'b'])
+
+   result.dtypes
+
+
 .. ipython:: python
    :suppress: