Update documentation to include 'column()' alias for 'col()' in DataFrame examples

Author: kosiew

docs/source/user-guide/dataframe/index.rst

@@ -142,7 +142,7 @@ For such methods, you can pass column names directly:
 
 .. code-block:: python
 
-    from datafusion import col, functions as f
+    from datafusion import col, column, functions as f
 
     df.sort('id')
     df.aggregate('id', [f.count(col('value'))])
@@ -151,11 +151,13 @@ The same operation can also be written with an explicit column expression:
 
 .. code-block:: python
 
-    from datafusion import col, functions as f
+    from datafusion import col, column, functions as f
 
     df.sort(col('id'))
     df.aggregate(col('id'), [f.count(col('value'))])
 
+Note that ``column()`` is an alias of ``col()``, so you can use either name.
+
 Whenever an argument represents an expression—such as in
 :py:meth:`~datafusion.DataFrame.filter` or
 :py:meth:`~datafusion.DataFrame.with_column`—use ``col()`` to reference columns